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TypeError: "x" is not a function - JavaScript | MDN

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for="sidebar-filter-input"><span class="icon icon-filter"></span><span class="visually-hidden">Filter sidebar</span></label><input id="sidebar-filter-input" autoComplete="off" class="sidebar-filter-input-field false" type="text" placeholder="Filter" value=""/><button type="button" class="button action has-icon clear-sidebar-filter-button"><span class="button-wrap"><span class="icon icon-cancel "></span><span class="visually-hidden">Clear filter input</span></span></button></div></section></header><div class="sidebar-inner-nav"><div class="in-nav-toc"><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#message">Message</a></li><li class="document-toc-item "><a class="document-toc-link" href="#error_type">Error type</a></li><li class="document-toc-item "><a class="document-toc-link" href="#what_went_wrong">What went wrong?</a></li><li class="document-toc-item "><a class="document-toc-link" href="#examples">Examples</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></div><div class="sidebar-body"> <ol> <li class="section"><a href="/en-US/docs/Web/JavaScript">JavaScript</a></li> <li class="section">Tutorials</li> <li class="toggle"> <details> <summary>Complete beginners</summary> <ol> <li><a href="/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics">JavaScript basics</a></li> <li><a href="/en-US/docs/Learn/JavaScript/First_steps">JavaScript first steps</a></li> <li><a href="/en-US/docs/Learn/JavaScript/Building_blocks">JavaScript building blocks</a></li> <li><a href="/en-US/docs/Learn/JavaScript/Objects">Introducing JavaScript objects</a></li> </ol> </details> </li> <li class="toggle"> <details> <summary>JavaScript Guide</summary> <ol> <li><a href="/en-US/docs/Web/JavaScript/Guide/Introduction">Introduction</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Grammar_and_types">Grammar and types</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Control_flow_and_error_handling">Control flow and error handling</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration">Loops and iteration</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Functions">Functions</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Expressions_and_operators">Expressions and operators</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Numbers_and_dates">Numbers and dates</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Text_formatting">Text formatting</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Regular_expressions">Regular expressions</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Indexed_collections">Indexed collections</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Keyed_collections">Keyed collections</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Working_with_objects">Working with objects</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Using_classes">Using classes</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Using_promises">Using promises</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Typed_arrays">JavaScript typed arrays</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Iterators_and_generators">Iterators and generators</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Meta_programming">Meta programming</a></li> <li><a href="/en-US/docs/Web/JavaScript/Guide/Modules">JavaScript modules</a></li> </ol> </details> </li> <li class="toggle"> <details> <summary>Intermediate</summary> <ol> <li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks">Client-side JavaScript frameworks</a></li> <li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs">Client-side web APIs</a></li> <li><a href="/en-US/docs/Web/JavaScript/Language_overview">Language overview</a></li> <li><a href="/en-US/docs/Web/JavaScript/Data_structures">JavaScript data structures</a></li> <li><a href="/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness">Equality comparisons and sameness</a></li> <li><a href="/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">Enumerability and ownership of properties</a></li> <li><a href="/en-US/docs/Web/JavaScript/Closures">Closures</a></li> </ol> </details> </li> <li class="toggle"> <details> <summary>Advanced</summary> <ol> <li><a href="/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain">Inheritance and the prototype chain</a></li> <li><a href="/en-US/docs/Web/JavaScript/Memory_management">Memory Management</a></li> <li><a href="/en-US/docs/Web/JavaScript/Event_loop">Concurrency model and Event Loop</a></li> </ol> </details> </li> <li class="section"><a href="/en-US/docs/Web/JavaScript/Reference">References</a></li> <li class="toggle"> <details> <summary>Built-in objects</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError">AggregateError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array">Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer">ArrayBuffer</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncFunction">AsyncFunction</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncGenerator">AsyncGenerator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncGeneratorFunction">AsyncGeneratorFunction</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncIterator">AsyncIterator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics">Atomics</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt">BigInt</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt64Array">BigInt64Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigUint64Array">BigUint64Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean">Boolean</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView">DataView</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date">Date</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURI">decodeURI()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURIComponent">decodeURIComponent()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI">encodeURI()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent">encodeURIComponent()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error">Error</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/escape">escape()</a><abbr class="icon icon-deprecated" title="Deprecated. Not for use in new websites."> <span class="visually-hidden">Deprecated</span> </abbr></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval">eval()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/EvalError">EvalError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/FinalizationRegistry">FinalizationRegistry</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float16Array">Float16Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array">Float32Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array">Float64Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function">Function</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Generator">Generator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/GeneratorFunction">GeneratorFunction</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis">globalThis</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Infinity">Infinity</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array">Int16Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array">Int32Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array">Int8Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/InternalError">InternalError</a><abbr class="icon icon-nonstandard" title="Non-standard. Check cross-browser support before using."> <span class="visually-hidden">Non-standard</span> </abbr></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl">Intl</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/isFinite">isFinite()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN">isNaN()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator">Iterator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON">JSON</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map">Map</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math">Math</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN">NaN</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">Number</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object">Object</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseFloat">parseFloat()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt">parseInt()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise">Promise</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy">Proxy</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/RangeError">RangeError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError">ReferenceError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect">Reflect</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp">RegExp</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set">Set</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer">SharedArrayBuffer</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/String">String</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol">Symbol</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/SyntaxError">SyntaxError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray">TypedArray</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError">TypeError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array">Uint16Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array">Uint32Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array">Uint8Array</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray">Uint8ClampedArray</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined">undefined</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/unescape">unescape()</a><abbr class="icon icon-deprecated" title="Deprecated. Not for use in new websites."> <span class="visually-hidden">Deprecated</span> </abbr></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/URIError">URIError</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap">WeakMap</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakRef">WeakRef</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet">WeakSet</a></li></ol> </details> </li> <li class="toggle"> <details> <summary>Expressions &amp; operators</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Addition">Addition (+)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Addition_assignment">Addition assignment (+=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Assignment">Assignment (=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/async_function">async function expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/async_function*">async function* expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/await">await</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_AND">Bitwise AND (&amp;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_AND_assignment">Bitwise AND assignment (&amp;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_NOT">Bitwise NOT (~)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_OR">Bitwise OR (|)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_OR_assignment">Bitwise OR assignment (|=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_XOR">Bitwise XOR (^)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_XOR_assignment">Bitwise XOR assignment (^=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/class">class expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Comma_operator">Comma operator (,)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator">Conditional (ternary) operator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Decrement">Decrement (--)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/delete">delete</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment">Destructuring assignment</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Division">Division (/)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Division_assignment">Division assignment (/=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Equality">Equality (==)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Exponentiation">Exponentiation (**)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Exponentiation_assignment">Exponentiation assignment (**=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/function">function expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/function*">function* expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Greater_than">Greater than (&gt;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Greater_than_or_equal">Greater than or equal (&gt;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Grouping">Grouping operator ( )</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/import.meta">import.meta</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/import">import()</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/in">in</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Increment">Increment (++)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Inequality">Inequality (!=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/instanceof">instanceof</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Left_shift">Left shift (&lt;&lt;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Left_shift_assignment">Left shift assignment (&lt;&lt;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Less_than">Less than (&lt;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Less_than_or_equal">Less than or equal (&lt;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Logical_AND">Logical AND (&amp;&amp;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Logical_AND_assignment">Logical AND assignment (&amp;&amp;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT">Logical NOT (!)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR">Logical OR (||)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR_assignment">Logical OR assignment (||=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Multiplication">Multiplication (*)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Multiplication_assignment">Multiplication assignment (*=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/new">new</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/new.target">new.target</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/null">null</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_assignment">Nullish coalescing assignment (??=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing">Nullish coalescing operator (??)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer">Object initializer</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Operator_precedence">Operator precedence</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining">Optional chaining (?.)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors">Property accessors</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Remainder">Remainder (%)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Remainder_assignment">Remainder assignment (%=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Right_shift">Right shift (&gt;&gt;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Right_shift_assignment">Right shift assignment (&gt;&gt;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax">Spread syntax (...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality">Strict equality (===)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Strict_inequality">Strict inequality (!==)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction">Subtraction (-)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction_assignment">Subtraction assignment (-=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/super">super</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/this">this</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/typeof">typeof</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Unary_negation">Unary negation (-)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Unary_plus">Unary plus (+)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Unsigned_right_shift">Unsigned right shift (&gt;&gt;&gt;)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Unsigned_right_shift_assignment">Unsigned right shift assignment (&gt;&gt;&gt;=)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/void">void operator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/yield">yield</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/yield*">yield*</a></li></ol> </details> </li> <li class="toggle"> <details> <summary>Statements &amp; declarations</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/async_function">async function</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/async_function*">async function*</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/block">Block statement</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/break">break</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/class">class</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/const">const</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/continue">continue</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/debugger">debugger</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/do...while">do...while</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/Empty">Empty statement</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/export">export</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/Expression_statement">Expression statement</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/for">for</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/for-await...of">for await...of</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/for...in">for...in</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/for...of">for...of</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/function">function</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/function*">function*</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/if...else">if...else</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/import">import</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/label">Labeled statement</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/let">let</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/return">return</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/switch">switch</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/throw">throw</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/try...catch">try...catch</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/var">var</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/while">while</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Statements/with">with</a><abbr class="icon icon-deprecated" title="Deprecated. Not for use in new websites."> <span class="visually-hidden">Deprecated</span> </abbr></li></ol> </details> </li> <li class="toggle"> <details> <summary>Functions</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions">Arrow function expressions</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters">Default parameters</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/get">get</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions">Method definitions</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters">Rest parameters</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/set">set</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Functions/arguments">The arguments object</a></li></ol> </details> </li> <li class="toggle"> <details> <summary>Classes</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes/constructor">constructor</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes/extends">extends</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes/Private_properties">Private properties</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes/Public_class_fields">Public class fields</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes/static">static</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Classes/Static_initialization_blocks">Static initialization blocks</a></li></ol> </details> </li> <li class="toggle"> <details> <summary>Regular expressions</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Backreference">Backreference: \1, \2</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Capturing_group">Capturing group: (...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class_escape">Character class escape: \d, \D, \w, \W, \s, \S</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class">Character class: [...], [^...]</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_escape">Character escape: \n, \u{...}</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Disjunction">Disjunction: |</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Input_boundary_assertion">Input boundary assertion: ^, $</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Literal_character">Literal character: a, b</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Lookahead_assertion">Lookahead assertion: (?=...), (?!...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Lookbehind_assertion">Lookbehind assertion: (?&lt;=...), (?&lt;!...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Modifier">Modifier: (?ims-ims:...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Named_backreference">Named backreference: \k&lt;name&gt;</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Named_capturing_group">Named capturing group: (?&lt;name&gt;...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Non-capturing_group">Non-capturing group: (?:...)</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Quantifier">Quantifier: *, +, ?, {n}, {n,}, {n,m}</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Unicode_character_class_escape">Unicode character class escape: \p{...}, \P{...}</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Wildcard">Wildcard: .</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Word_boundary_assertion">Word boundary assertion: \b, \B</a></li></ol> </details> </li> <li class="toggle"> <details open=""> <summary>Errors</summary> <ol><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors">Overview</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Promise_any_all_rejected">AggregateError: No Promise in Promise.any was resolved</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Property_access_denied">Error: Permission denied to access property "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Too_much_recursion">InternalError: too much recursion</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_valid_code_point">RangeError: argument is not a valid code point</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/BigInt_division_by_zero">RangeError: BigInt division by zero</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/BigInt_negative_exponent">RangeError: BigInt negative exponent</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Form_must_be_one_of">RangeError: form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD'</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_array_length">RangeError: invalid array length</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_date">RangeError: invalid date</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Precision_range">RangeError: precision is out of range</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_radix">RangeError: radix must be an integer</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Resulting_string_too_large">RangeError: repeat count must be less than infinity</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Negative_repetition_count">RangeError: repeat count must be non-negative</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_be_converted_to_BigInt_because_it_isnt_an_integer">RangeError: x can't be converted to BigInt because it isn't an integer</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Not_defined">ReferenceError: "x" is not defined</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Undeclared_var">ReferenceError: assignment to undeclared variable "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_access_lexical_declaration_before_init">ReferenceError: can't access lexical declaration 'X' before initialization</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_caller_or_arguments_usage">ReferenceError: deprecated caller or arguments usage</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Super_not_called">ReferenceError: must call super constructor before using 'this' in derived class constructor</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Super_called_twice">ReferenceError: super() called twice in derived class constructor</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_strict_arguments_eval">SyntaxError: 'arguments'/'eval' can't be defined or assigned to in strict mode code</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_octal_literal">SyntaxError: "0"-prefixed octal literals are deprecated</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Strict_non_simple_params">SyntaxError: "use strict" not allowed in function with non-simple parameters</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Reserved_identifier">SyntaxError: "x" is a reserved identifier</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_backslash_at_end_of_pattern">SyntaxError: \ at end of pattern</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_for-of_initializer">SyntaxError: a declaration in the head of a for-of loop can't have an initializer</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Delete_in_strict_mode">SyntaxError: applying the 'delete' operator to an unqualified name is deprecated</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Arguments_not_allowed">SyntaxError: arguments is not valid in fields</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_await">SyntaxError: await is only valid in async functions, async generators and modules</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/await_yield_in_parameter">SyntaxError: await/yield expression can't be used in parameter</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_use_nullish_coalescing_unparenthesized">SyntaxError: cannot use `??` unparenthesized within `||` and `&amp;&amp;` expressions</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_character_class_escape_in_class_range">SyntaxError: character class escape cannot be used in class range in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_continue">SyntaxError: continue must be inside loop</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_duplicate_capture_group_name">SyntaxError: duplicate capture group name in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Duplicate_parameter">SyntaxError: duplicate formal argument x</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_for-in_initializer">SyntaxError: for-in loop head declarations may not have initializers</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Unnamed_function_statement">SyntaxError: function statement requires a name</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Function_label">SyntaxError: functions cannot be labelled</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Either_be_both_static_or_non-static">SyntaxError: getter and setter for private name #x should either be both static or non-static</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Getter_no_arguments">SyntaxError: getter functions must have no arguments</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Identifier_after_number">SyntaxError: identifier starts immediately after numeric literal</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Illegal_character">SyntaxError: illegal character</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/import_decl_module_top_level">SyntaxError: import declarations may only appear at top level of a module</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_incomplete_quantifier">SyntaxError: incomplete quantifier in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_assignment_left-hand_side">SyntaxError: invalid assignment left-hand side</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_BigInt_syntax">SyntaxError: invalid BigInt syntax</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_capture_group_name">SyntaxError: invalid capture group name in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_char_in_class">SyntaxError: invalid character in class in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_class_set_operation">SyntaxError: invalid class set operation in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_decimal_escape">SyntaxError: invalid decimal escape in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_identity_escape">SyntaxError: invalid identity escape in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_named_capture_reference">SyntaxError: invalid named capture reference in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_property_name">SyntaxError: invalid property name in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_range_in_character_class">SyntaxError: invalid range in character class</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_group">SyntaxError: invalid regexp group</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_regexp_flag">SyntaxError: invalid regular expression flag "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_unicode_escape">SyntaxError: invalid unicode escape in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/JSON_bad_parse">SyntaxError: JSON.parse: bad parsing</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Label_not_found">SyntaxError: label not found</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_colon_after_property_id">SyntaxError: missing : after property id</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_parenthesis_after_argument_list">SyntaxError: missing ) after argument list</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_parenthesis_after_condition">SyntaxError: missing ) after condition</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_bracket_after_list">SyntaxError: missing ] after element list</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_curly_after_function_body">SyntaxError: missing } after function body</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_curly_after_property_list">SyntaxError: missing } after property list</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_initializer_in_const">SyntaxError: missing = in const declaration</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_formal_parameter">SyntaxError: missing formal parameter</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Missing_name_after_dot_operator">SyntaxError: missing name after . operator</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/No_variable_name">SyntaxError: missing variable name</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_negated_char_class_with_strings">SyntaxError: negated character class with strings in regular expression</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_new_optional">SyntaxError: new keyword cannot be used with an optional chain</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_nothing_to_repeat">SyntaxError: nothing to repeat</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_numbers_out_of_order_in_quantifier">SyntaxError: numbers out of order in {} quantifier.</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_octal_escape_sequence">SyntaxError: octal escape sequences can't be used in untagged template literals or in strict mode code</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Parameter_after_rest_parameter">SyntaxError: parameter after rest parameter</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_delete_private_fields">SyntaxError: private fields can't be deleted</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Duplicate_proto">SyntaxError: property name __proto__ appears more than once in object literal</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Regex_raw_bracket">SyntaxError: raw bracket is not allowed in regular expression with unicode flag</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Redeclared_parameter">SyntaxError: redeclaration of formal parameter "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Undeclared_private_field_or_method">SyntaxError: reference to undeclared private field or method #x</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Rest_with_default">SyntaxError: rest parameter may not have a default</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_return">SyntaxError: return not in function</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Setter_one_argument">SyntaxError: setter functions must have one argument</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/String_literal_EOL">SyntaxError: string literal contains an unescaped line break</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_super_call">SyntaxError: super() is only valid in derived class constructors</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_optional_template">SyntaxError: tagged template cannot be used with optional chain</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Hash_outside_class">SyntaxError: Unexpected '#' used outside of class body</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Unexpected_token">SyntaxError: Unexpected token</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_break">SyntaxError: unlabeled break must be inside loop or switch</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Unparenthesized_unary_expr_lhs_exponentiation">SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**'</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Bad_super_prop">SyntaxError: use of super property/member accesses only valid within methods or eval code within methods</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_source_map_pragma">SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/is_not_iterable">TypeError: 'x' is not iterable</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Unexpected_type">TypeError: "x" is (not) "y"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_constructor">TypeError: "x" is not a constructor</a></li><li><em><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_function" aria-current="page">TypeError: "x" is not a function</a></em></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/No_non-null_object">TypeError: "x" is not a non-null object</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Read-only">TypeError: "x" is read-only</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/BigInt_not_serializable">TypeError: BigInt value can't be serialized in JSON</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Builtin_ctor_no_new">TypeError: calling a builtin X constructor without new is forbidden</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Get_set_missing_private">TypeError: can't access/set private field or method: object is not the right class</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_assign_to_property">TypeError: can't assign to property "x" on "y": not an object</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_convert_BigInt_to_number">TypeError: can't convert BigInt to number</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_convert_x_to_BigInt">TypeError: can't convert x to BigInt</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_define_property_object_not_extensible">TypeError: can't define property "x": "obj" is not extensible</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Non_configurable_array_element">TypeError: can't delete non-configurable array element</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_redefine_property">TypeError: can't redefine non-configurable property "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_set_prototype">TypeError: can't set prototype of this object</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_prototype">TypeError: can't set prototype: it would cause a prototype chain cycle</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/in_operator_no_object">TypeError: cannot use 'in' operator to search for 'x' in 'y'</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Class_ctor_no_new">TypeError: class constructors must be invoked with 'new'</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_object_value">TypeError: cyclic object value</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_derived_return">TypeError: derived class constructor returned invalid value x</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Private_setter_only">TypeError: getting private setter-only property</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Private_double_initialization">TypeError: Initializing an object twice is an error with private fields/methods</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/invalid_right_hand_side_instanceof_operand">TypeError: invalid 'instanceof' operand 'x'</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Array_sort_argument">TypeError: invalid Array.prototype.sort argument</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_const_assignment">TypeError: invalid assignment to const "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Constructor_cant_be_used_directly">TypeError: Iterator/AsyncIterator constructor can't be used directly</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Requires_global_RegExp">TypeError: matchAll/replaceAll must be called with a global RegExp</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/More_arguments_needed">TypeError: More arguments needed</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/No_properties">TypeError: null/undefined has no properties</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Cant_delete">TypeError: property "x" is non-configurable and can't be deleted</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Reduce_of_empty_array_with_no_initial_value">TypeError: Reduce of empty array with no initial value</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Getter_only">TypeError: setting getter-only property "x"</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Key_not_weakly_held">TypeError: WeakSet key/WeakMap value 'x' must be an object or an unregistered symbol</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Called_on_incompatible_type">TypeError: X.prototype.y called on incompatible type</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Malformed_URI">URIError: malformed URI sequence</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Already_has_pragma">Warning: -file- is being assigned a //# sourceMappingURL, but already has one</a></li><li><a href="/en-US/docs/Web/JavaScript/Reference/Errors/Stmt_after_return">Warning: unreachable code after return statement</a></li></ol> </details> </li> <li class="toggle"> <details> <summary>Misc</summary> <ol> <li><a href="/en-US/docs/Web/JavaScript/JavaScript_technologies_overview">JavaScript technologies overview</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Lexical_grammar">Lexical grammar</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Iteration_protocols">Iteration protocols</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Strict_mode">Strict mode</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Template_literals">Template literals</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Trailing_commas">Trailing commas</a></li> <li><a href="/en-US/docs/Web/JavaScript/Reference/Deprecated_and_obsolete_features">Deprecated features</a></li> </ol> </details> </li> </ol> </div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#message">Message</a></li><li class="document-toc-item "><a class="document-toc-link" href="#error_type">Error type</a></li><li class="document-toc-item "><a class="document-toc-link" href="#what_went_wrong">What went wrong?</a></li><li class="document-toc-item "><a class="document-toc-link" href="#examples">Examples</a></li><li class="document-toc-item "><a class="document-toc-link" href="#see_also">See also</a></li></ul></section></div></nav></aside><section class="place side"></section></div></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>TypeError: &quot;x&quot; is not a function</h1></header><div class="section-content"><p> The JavaScript exception "is not a function" occurs when there was an attempt to call a value from a function, but the value is not actually a function. </p></div><section aria-labelledby="message"><h2 id="message"><a href="#message">Message</a></h2><div class="section-content"><pre class="brush: plain notranslate">TypeError: "x" is not a function. (V8-based &amp; Firefox &amp; Safari) </pre></div></section><section aria-labelledby="error_type"><h2 id="error_type"><a href="#error_type">Error type</a></h2><div class="section-content"><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError"><code>TypeError</code></a></div></section><section aria-labelledby="what_went_wrong"><h2 id="what_went_wrong"><a href="#what_went_wrong">What went wrong?</a></h2><div class="section-content"><p> It attempted to call a value from a function, but the value is not actually a function. Some code expects you to provide a function, but that didn't happen. </p> <p> Maybe there is a typo in the function name? Maybe the object you are calling the method on does not have this function? For example, JavaScript <code>Objects</code> have no <code>map</code> function, but the JavaScript <code>Array</code> object does. </p> <p> There are many built-in functions in need of a (callback) function. You will have to provide a function in order to have these methods working properly: </p> <ul> <li> <p>When working with <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array"><code>Array</code></a> or <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> objects:</p> <ul> <li> <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every"><code>Array.prototype.every()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some"><code>Array.prototype.some()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach"><code>Array.prototype.forEach()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map"><code>Array.prototype.map()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter"><code>Array.prototype.filter()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce"><code>Array.prototype.reduce()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduceRight"><code>Array.prototype.reduceRight()</code></a>, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find"><code>Array.prototype.find()</code></a> </li> </ul> </li> <li> <p>When working with <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> and <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> objects:</p> <ul> <li><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/forEach"><code>Map.prototype.forEach()</code></a> and <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/forEach"><code>Set.prototype.forEach()</code></a></li> </ul> </li> </ul></div></section><section aria-labelledby="examples"><h2 id="examples"><a href="#examples">Examples</a></h2><div class="section-content"></div></section><section aria-labelledby="a_typo_in_the_function_name"><h3 id="a_typo_in_the_function_name"><a href="#a_typo_in_the_function_name">A typo in the function name</a></h3><div class="section-content"><p>In this case, which happens way too often, there is a typo in the method name:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-bad notranslate"><code>const x = document.getElementByID("foo"); // TypeError: document.getElementByID is not a function </code></pre></div> <p>The correct function name is <code>getElementById</code>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-good notranslate"><code>const x = document.getElementById("foo"); </code></pre></div></div></section><section aria-labelledby="function_called_on_the_wrong_object"><h3 id="function_called_on_the_wrong_object"><a href="#function_called_on_the_wrong_object">Function called on the wrong object</a></h3><div class="section-content"><p> For certain methods, you have to provide a (callback) function and it will work on specific objects only. In this example, <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map"><code>Array.prototype.map()</code></a> is used, which will work with <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array"><code>Array</code></a> objects only. </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-bad notranslate"><code>const obj = { a: 13, b: 37, c: 42 }; obj.map(function (num) { return num * 2; }); // TypeError: obj.map is not a function </code></pre></div> <p>Use an array instead:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-good notranslate"><code>const numbers = [1, 4, 9]; numbers.map(function (num) { return num * 2; }); // [2, 8, 18] </code></pre></div></div></section><section aria-labelledby="function_shares_a_name_with_a_pre-existing_property"><h3 id="function_shares_a_name_with_a_pre-existing_property"><a href="#function_shares_a_name_with_a_pre-existing_property">Function shares a name with a pre-existing property</a></h3><div class="section-content"><p> Sometimes when making a class, you may have a property and a function with the same name. Upon calling the function, the compiler thinks that the function ceases to exist. </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-bad notranslate"><code>function Dog() { this.age = 11; this.color = "black"; this.name = "Ralph"; return this; } Dog.prototype.name = function (name) { this.name = name; return this; }; const myNewDog = new Dog(); myNewDog.name("Cassidy"); //Uncaught TypeError: myNewDog.name is not a function </code></pre></div> <p>Use a different property name instead:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-good notranslate"><code>function Dog() { this.age = 11; this.color = "black"; this.dogName = "Ralph"; //Using this.dogName instead of .name return this; } Dog.prototype.name = function (name) { this.dogName = name; return this; }; const myNewDog = new Dog(); myNewDog.name("Cassidy"); //Dog { age: 11, color: 'black', dogName: 'Cassidy' } </code></pre></div></div></section><section aria-labelledby="using_parentheses_for_multiplication"><h3 id="using_parentheses_for_multiplication"><a href="#using_parentheses_for_multiplication">Using parentheses for multiplication</a></h3><div class="section-content"><p>In math, you can write 2 × (3 + 5) as 2*(3 + 5) or just 2(3 + 5).</p> <p>Using the latter will throw an error:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-bad notranslate"><code>const sixteen = 2(3 + 5); console.log(`2 x (3 + 5) is ${sixteen}`); // Uncaught TypeError: 2 is not a function </code></pre></div> <p>You can correct the code by adding a <code>*</code> operator:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js example-good notranslate"><code>const sixteen = 2 * (3 + 5); console.log(`2 x (3 + 5) is ${sixteen}`); // 2 x (3 + 5) is 16 </code></pre></div></div></section><section aria-labelledby="import_the_exported_module_correctly"><h3 id="import_the_exported_module_correctly"><a href="#import_the_exported_module_correctly">Import the exported module correctly</a></h3><div class="section-content"><p>Ensure you are importing the module correctly.</p> <p>An example helpers library (<code>helpers.js</code>)</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const helpers = function () {}; helpers.groupBy = function (objectArray, property) { return objectArray.reduce((acc, obj) =&gt; { const key = obj[property]; acc[key] ??= []; acc[key].push(obj); return acc; }, {}); }; export default helpers; </code></pre></div> <p>The correct import usage (<code>App.js</code>):</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>import helpers from "./helpers"; </code></pre></div></div></section><section aria-labelledby="see_also"><h2 id="see_also"><a href="#see_also">See also</a></h2><div class="section-content"><ul> <li><a href="/en-US/docs/Web/JavaScript/Reference/Functions">Functions</a></li> </ul></div></section></article><aside class="article-footer"><div class="article-footer-inner"><div class="svg-container"><svg xmlns="http://www.w3.org/2000/svg" width="162" height="162" viewBox="0 0 162 162" fill="none" role="none"><mask id="b" fill="#fff"><path d="M97.203 47.04c8.113-7.886 18.004-13.871 28.906-17.492a78 78 0 0 1 33.969-3.39c11.443 1.39 22.401 5.295 32.024 11.411s17.656 14.28 23.476 23.86c5.819 9.579 9.269 20.318 10.083 31.385a69.85 69.85 0 0 1-5.387 32.44c-4.358 10.272-11.115 19.443-19.747 26.801-8.632 7.359-18.908 12.709-30.034 15.637l-6.17-21.698c7.666-2.017 14.746-5.703 20.694-10.773 5.948-5.071 10.603-11.389 13.606-18.467a48.14 48.14 0 0 0 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href=\"/en-US/docs/Web/JavaScript/Guide/Text_formatting\">Text formatting</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Regular_expressions\">Regular expressions</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Indexed_collections\">Indexed collections</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Keyed_collections\">Keyed collections</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Working_with_objects\">Working with objects</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Using_classes\">Using classes</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Using_promises\">Using promises</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Typed_arrays\">JavaScript typed arrays</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Iterators_and_generators\">Iterators and generators</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Meta_programming\">Meta programming</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Guide/Modules\">JavaScript modules</a></li>\n </ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Intermediate</summary>\n <ol>\n <li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks\">Client-side JavaScript frameworks</a></li>\n <li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs\">Client-side web APIs</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Language_overview\">Language overview</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Data_structures\">JavaScript data structures</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness\">Equality comparisons and sameness</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties\">Enumerability and ownership of properties</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Closures\">Closures</a></li>\n </ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n 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href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncFunction\">AsyncFunction</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncGenerator\">AsyncGenerator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncGeneratorFunction\">AsyncGeneratorFunction</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/AsyncIterator\">AsyncIterator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics\">Atomics</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt\">BigInt</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt64Array\">BigInt64Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigUint64Array\">BigUint64Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean\">Boolean</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView\">DataView</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date\">Date</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURI\">decodeURI()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURIComponent\">decodeURIComponent()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI\">encodeURI()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent\">encodeURIComponent()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error\">Error</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/escape\">escape()</a><abbr class=\"icon icon-deprecated\" title=\"Deprecated. Not for use in new websites.\">\n <span class=\"visually-hidden\">Deprecated</span>\n</abbr></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval\">eval()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/EvalError\">EvalError</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/FinalizationRegistry\">FinalizationRegistry</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float16Array\">Float16Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array\">Float32Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array\">Float64Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function\">Function</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Generator\">Generator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/GeneratorFunction\">GeneratorFunction</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis\">globalThis</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Infinity\">Infinity</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array\">Int16Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array\">Int32Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array\">Int8Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/InternalError\">InternalError</a><abbr class=\"icon icon-nonstandard\" title=\"Non-standard. Check cross-browser support before using.\">\n <span class=\"visually-hidden\">Non-standard</span>\n</abbr></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl\">Intl</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/isFinite\">isFinite()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN\">isNaN()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator\">Iterator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON\">JSON</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map\">Map</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math\">Math</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN\">NaN</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number\">Number</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object\">Object</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseFloat\">parseFloat()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt\">parseInt()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise\">Promise</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy\">Proxy</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/RangeError\">RangeError</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/ReferenceError\">ReferenceError</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect\">Reflect</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp\">RegExp</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set\">Set</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer\">SharedArrayBuffer</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/String\">String</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol\">Symbol</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/SyntaxError\">SyntaxError</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray\">TypedArray</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError\">TypeError</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array\">Uint16Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array\">Uint32Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array\">Uint8Array</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray\">Uint8ClampedArray</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined\">undefined</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/unescape\">unescape()</a><abbr class=\"icon icon-deprecated\" title=\"Deprecated. Not for use in new websites.\">\n <span class=\"visually-hidden\">Deprecated</span>\n</abbr></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/URIError\">URIError</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap\">WeakMap</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakRef\">WeakRef</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet\">WeakSet</a></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Expressions &amp; operators</summary>\n <ol><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators\">Overview</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Addition\">Addition (+)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Addition_assignment\">Addition assignment (+=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Assignment\">Assignment (=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/async_function\">async function expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/async_function*\">async function* expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/await\">await</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_AND\">Bitwise AND (&amp;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_AND_assignment\">Bitwise AND assignment (&amp;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_NOT\">Bitwise NOT (~)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_OR\">Bitwise OR (|)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_OR_assignment\">Bitwise OR assignment (|=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_XOR\">Bitwise XOR (^)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_XOR_assignment\">Bitwise XOR assignment (^=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/class\">class expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Comma_operator\">Comma operator (,)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator\">Conditional (ternary) operator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Decrement\">Decrement (--)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/delete\">delete</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment\">Destructuring assignment</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Division\">Division (/)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Division_assignment\">Division assignment (/=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Equality\">Equality (==)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Exponentiation\">Exponentiation (**)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Exponentiation_assignment\">Exponentiation assignment (**=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/function\">function expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/function*\">function* expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Greater_than\">Greater than (&gt;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Greater_than_or_equal\">Greater than or equal (&gt;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Grouping\">Grouping operator ( )</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/import.meta\">import.meta</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/import\">import()</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/in\">in</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Increment\">Increment (++)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Inequality\">Inequality (!=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/instanceof\">instanceof</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Left_shift\">Left shift (&lt;&lt;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Left_shift_assignment\">Left shift assignment (&lt;&lt;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Less_than\">Less than (&lt;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Less_than_or_equal\">Less than or equal (&lt;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Logical_AND\">Logical AND (&amp;&amp;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Logical_AND_assignment\">Logical AND assignment (&amp;&amp;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT\">Logical NOT (!)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR\">Logical OR (||)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR_assignment\">Logical OR assignment (||=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Multiplication\">Multiplication (*)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Multiplication_assignment\">Multiplication assignment (*=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/new\">new</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/new.target\">new.target</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/null\">null</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_assignment\">Nullish coalescing assignment (??=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing\">Nullish coalescing operator (??)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer\">Object initializer</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Operator_precedence\">Operator precedence</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining\">Optional chaining (?.)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Property_accessors\">Property accessors</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Remainder\">Remainder (%)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Remainder_assignment\">Remainder assignment (%=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Right_shift\">Right shift (&gt;&gt;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Right_shift_assignment\">Right shift assignment (&gt;&gt;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax\">Spread syntax (...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality\">Strict equality (===)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Strict_inequality\">Strict inequality (!==)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction\">Subtraction (-)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Subtraction_assignment\">Subtraction assignment (-=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/super\">super</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/this\">this</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/typeof\">typeof</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Unary_negation\">Unary negation (-)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Unary_plus\">Unary plus (+)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Unsigned_right_shift\">Unsigned right shift (&gt;&gt;&gt;)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/Unsigned_right_shift_assignment\">Unsigned right shift assignment (&gt;&gt;&gt;=)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/void\">void operator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/yield\">yield</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/yield*\">yield*</a></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Statements &amp; declarations</summary>\n <ol><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements\">Overview</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/async_function\">async function</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/async_function*\">async function*</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/block\">Block statement</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/break\">break</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/class\">class</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/const\">const</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/continue\">continue</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/debugger\">debugger</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/do...while\">do...while</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/Empty\">Empty statement</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/export\">export</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/Expression_statement\">Expression statement</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/for\">for</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/for-await...of\">for await...of</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/for...in\">for...in</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/for...of\">for...of</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/function\">function</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/function*\">function*</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/if...else\">if...else</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/import\">import</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/label\">Labeled statement</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/let\">let</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/return\">return</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/switch\">switch</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/throw\">throw</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/try...catch\">try...catch</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/var\">var</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/while\">while</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/with\">with</a><abbr class=\"icon icon-deprecated\" title=\"Deprecated. Not for use in new websites.\">\n <span class=\"visually-hidden\">Deprecated</span>\n</abbr></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Functions</summary>\n <ol><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions\">Overview</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions\">Arrow function expressions</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters\">Default parameters</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/get\">get</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions\">Method definitions</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters\">Rest parameters</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/set\">set</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions/arguments\">The arguments object</a></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Classes</summary>\n <ol><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes\">Overview</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/constructor\">constructor</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/extends\">extends</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/Private_properties\">Private properties</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/Public_class_fields\">Public class fields</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/static\">static</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/Static_initialization_blocks\">Static initialization blocks</a></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Regular expressions</summary>\n <ol><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions\">Overview</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Backreference\">Backreference: \\1, \\2</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Capturing_group\">Capturing group: (...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class_escape\">Character class escape: \\d, \\D, \\w, \\W, \\s, \\S</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class\">Character class: [...], [^...]</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_escape\">Character escape: \\n, \\u{...}</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Disjunction\">Disjunction: |</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Input_boundary_assertion\">Input boundary assertion: ^, $</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Literal_character\">Literal character: a, b</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Lookahead_assertion\">Lookahead assertion: (?=...), (?!...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Lookbehind_assertion\">Lookbehind assertion: (?&lt;=...), (?&lt;!...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Modifier\">Modifier: (?ims-ims:...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Named_backreference\">Named backreference: \\k&lt;name&gt;</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Named_capturing_group\">Named capturing group: (?&lt;name&gt;...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Non-capturing_group\">Non-capturing group: (?:...)</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Quantifier\">Quantifier: *, +, ?, {n}, {n,}, {n,m}</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Unicode_character_class_escape\">Unicode character class escape: \\p{...}, \\P{...}</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Wildcard\">Wildcard: .</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Word_boundary_assertion\">Word boundary assertion: \\b, \\B</a></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details open=\"\">\n <summary>Errors</summary>\n <ol><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors\">Overview</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Promise_any_all_rejected\">AggregateError: No Promise in Promise.any was resolved</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Property_access_denied\">Error: Permission denied to access property \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Too_much_recursion\">InternalError: too much recursion</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_valid_code_point\">RangeError: argument is not a valid code point</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/BigInt_division_by_zero\">RangeError: BigInt division by zero</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/BigInt_negative_exponent\">RangeError: BigInt negative exponent</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Form_must_be_one_of\">RangeError: form must be one of 'NFC', 'NFD', 'NFKC', or 'NFKD'</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_array_length\">RangeError: invalid array length</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_date\">RangeError: invalid date</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Precision_range\">RangeError: precision is out of range</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_radix\">RangeError: radix must be an integer</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Resulting_string_too_large\">RangeError: repeat count must be less than infinity</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Negative_repetition_count\">RangeError: repeat count must be non-negative</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_be_converted_to_BigInt_because_it_isnt_an_integer\">RangeError: x can't be converted to BigInt because it isn't an integer</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Not_defined\">ReferenceError: \"x\" is not defined</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Undeclared_var\">ReferenceError: assignment to undeclared variable \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_access_lexical_declaration_before_init\">ReferenceError: can't access lexical declaration 'X' before initialization</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_caller_or_arguments_usage\">ReferenceError: deprecated caller or arguments usage</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Super_not_called\">ReferenceError: must call super constructor before using 'this' in derived class constructor</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Super_called_twice\">ReferenceError: super() called twice in derived class constructor</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_strict_arguments_eval\">SyntaxError: 'arguments'/'eval' can't be defined or assigned to in strict mode code</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_octal_literal\">SyntaxError: \"0\"-prefixed octal literals are deprecated</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Strict_non_simple_params\">SyntaxError: \"use strict\" not allowed in function with non-simple parameters</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Reserved_identifier\">SyntaxError: \"x\" is a reserved identifier</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_backslash_at_end_of_pattern\">SyntaxError: \\ at end of pattern</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_for-of_initializer\">SyntaxError: a declaration in the head of a for-of loop can't have an initializer</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Delete_in_strict_mode\">SyntaxError: applying the 'delete' operator to an unqualified name is deprecated</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Arguments_not_allowed\">SyntaxError: arguments is not valid in fields</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_await\">SyntaxError: await is only valid in async functions, async generators and modules</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/await_yield_in_parameter\">SyntaxError: await/yield expression can't be used in parameter</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_use_nullish_coalescing_unparenthesized\">SyntaxError: cannot use `??` unparenthesized within `||` and `&amp;&amp;` expressions</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_character_class_escape_in_class_range\">SyntaxError: character class escape cannot be used in class range in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_continue\">SyntaxError: continue must be inside loop</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_duplicate_capture_group_name\">SyntaxError: duplicate capture group name in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Duplicate_parameter\">SyntaxError: duplicate formal argument x</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_for-in_initializer\">SyntaxError: for-in loop head declarations may not have initializers</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Unnamed_function_statement\">SyntaxError: function statement requires a name</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Function_label\">SyntaxError: functions cannot be labelled</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Either_be_both_static_or_non-static\">SyntaxError: getter and setter for private name #x should either be both static or non-static</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Getter_no_arguments\">SyntaxError: getter functions must have no arguments</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Identifier_after_number\">SyntaxError: identifier starts immediately after numeric literal</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Illegal_character\">SyntaxError: illegal character</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/import_decl_module_top_level\">SyntaxError: import declarations may only appear at top level of a module</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_incomplete_quantifier\">SyntaxError: incomplete quantifier in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_assignment_left-hand_side\">SyntaxError: invalid assignment left-hand side</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_BigInt_syntax\">SyntaxError: invalid BigInt syntax</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_capture_group_name\">SyntaxError: invalid capture group name in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_char_in_class\">SyntaxError: invalid character in class in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_class_set_operation\">SyntaxError: invalid class set operation in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_decimal_escape\">SyntaxError: invalid decimal escape in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_identity_escape\">SyntaxError: invalid identity escape in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_named_capture_reference\">SyntaxError: invalid named capture reference in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_property_name\">SyntaxError: invalid property name in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_range_in_character_class\">SyntaxError: invalid range in character class</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_group\">SyntaxError: invalid regexp group</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_regexp_flag\">SyntaxError: invalid regular expression flag \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_unicode_escape\">SyntaxError: invalid unicode escape in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/JSON_bad_parse\">SyntaxError: JSON.parse: bad parsing</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Label_not_found\">SyntaxError: label not found</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_colon_after_property_id\">SyntaxError: missing : after property id</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_parenthesis_after_argument_list\">SyntaxError: missing ) after argument list</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_parenthesis_after_condition\">SyntaxError: missing ) after condition</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_bracket_after_list\">SyntaxError: missing ] after element list</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_curly_after_function_body\">SyntaxError: missing } after function body</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_curly_after_property_list\">SyntaxError: missing } after property list</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_initializer_in_const\">SyntaxError: missing = in const declaration</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_formal_parameter\">SyntaxError: missing formal parameter</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Missing_name_after_dot_operator\">SyntaxError: missing name after . operator</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/No_variable_name\">SyntaxError: missing variable name</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_negated_char_class_with_strings\">SyntaxError: negated character class with strings in regular expression</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_new_optional\">SyntaxError: new keyword cannot be used with an optional chain</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_nothing_to_repeat\">SyntaxError: nothing to repeat</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_numbers_out_of_order_in_quantifier\">SyntaxError: numbers out of order in {} quantifier.</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_octal_escape_sequence\">SyntaxError: octal escape sequences can't be used in untagged template literals or in strict mode code</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Parameter_after_rest_parameter\">SyntaxError: parameter after rest parameter</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_delete_private_fields\">SyntaxError: private fields can't be deleted</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Duplicate_proto\">SyntaxError: property name __proto__ appears more than once in object literal</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Regex_raw_bracket\">SyntaxError: raw bracket is not allowed in regular expression with unicode flag</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Redeclared_parameter\">SyntaxError: redeclaration of formal parameter \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Undeclared_private_field_or_method\">SyntaxError: reference to undeclared private field or method #x</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Rest_with_default\">SyntaxError: rest parameter may not have a default</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_return\">SyntaxError: return not in function</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Setter_one_argument\">SyntaxError: setter functions must have one argument</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/String_literal_EOL\">SyntaxError: string literal contains an unescaped line break</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_super_call\">SyntaxError: super() is only valid in derived class constructors</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_optional_template\">SyntaxError: tagged template cannot be used with optional chain</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Hash_outside_class\">SyntaxError: Unexpected '#' used outside of class body</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Unexpected_token\">SyntaxError: Unexpected token</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_break\">SyntaxError: unlabeled break must be inside loop or switch</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Unparenthesized_unary_expr_lhs_exponentiation\">SyntaxError: unparenthesized unary expression can't appear on the left-hand side of '**'</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Bad_super_prop\">SyntaxError: use of super property/member accesses only valid within methods or eval code within methods</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_source_map_pragma\">SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/is_not_iterable\">TypeError: 'x' is not iterable</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Unexpected_type\">TypeError: \"x\" is (not) \"y\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_constructor\">TypeError: \"x\" is not a constructor</a></li><li><em><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_function\" aria-current=\"page\">TypeError: \"x\" is not a function</a></em></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/No_non-null_object\">TypeError: \"x\" is not a non-null object</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Read-only\">TypeError: \"x\" is read-only</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/BigInt_not_serializable\">TypeError: BigInt value can't be serialized in JSON</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Builtin_ctor_no_new\">TypeError: calling a builtin X constructor without new is forbidden</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Get_set_missing_private\">TypeError: can't access/set private field or method: object is not the right class</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_assign_to_property\">TypeError: can't assign to property \"x\" on \"y\": not an object</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_convert_BigInt_to_number\">TypeError: can't convert BigInt to number</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_convert_x_to_BigInt\">TypeError: can't convert x to BigInt</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_define_property_object_not_extensible\">TypeError: can't define property \"x\": \"obj\" is not extensible</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Non_configurable_array_element\">TypeError: can't delete non-configurable array element</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_redefine_property\">TypeError: can't redefine non-configurable property \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_set_prototype\">TypeError: can't set prototype of this object</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_prototype\">TypeError: can't set prototype: it would cause a prototype chain cycle</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/in_operator_no_object\">TypeError: cannot use 'in' operator to search for 'x' in 'y'</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Class_ctor_no_new\">TypeError: class constructors must be invoked with 'new'</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_object_value\">TypeError: cyclic object value</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_derived_return\">TypeError: derived class constructor returned invalid value x</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Private_setter_only\">TypeError: getting private setter-only property</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Private_double_initialization\">TypeError: Initializing an object twice is an error with private fields/methods</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/invalid_right_hand_side_instanceof_operand\">TypeError: invalid 'instanceof' operand 'x'</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Array_sort_argument\">TypeError: invalid Array.prototype.sort argument</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_const_assignment\">TypeError: invalid assignment to const \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Constructor_cant_be_used_directly\">TypeError: Iterator/AsyncIterator constructor can't be used directly</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Requires_global_RegExp\">TypeError: matchAll/replaceAll must be called with a global RegExp</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/More_arguments_needed\">TypeError: More arguments needed</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/No_properties\">TypeError: null/undefined has no properties</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Cant_delete\">TypeError: property \"x\" is non-configurable and can't be deleted</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Reduce_of_empty_array_with_no_initial_value\">TypeError: Reduce of empty array with no initial value</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Getter_only\">TypeError: setting getter-only property \"x\"</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Key_not_weakly_held\">TypeError: WeakSet key/WeakMap value 'x' must be an object or an unregistered symbol</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Called_on_incompatible_type\">TypeError: X.prototype.y called on incompatible type</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Malformed_URI\">URIError: malformed URI sequence</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Already_has_pragma\">Warning: -file- is being assigned a //# sourceMappingURL, but already has one</a></li><li><a href=\"/en-US/docs/Web/JavaScript/Reference/Errors/Stmt_after_return\">Warning: unreachable code after return statement</a></li></ol>\n </details>\n </li>\n <li class=\"toggle\">\n <details>\n <summary>Misc</summary>\n <ol>\n <li><a href=\"/en-US/docs/Web/JavaScript/JavaScript_technologies_overview\">JavaScript technologies overview</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Lexical_grammar\">Lexical grammar</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Iteration_protocols\">Iteration protocols</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Strict_mode\">Strict mode</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Template_literals\">Template literals</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Trailing_commas\">Trailing commas</a></li>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Deprecated_and_obsolete_features\">Deprecated features</a></li>\n </ol>\n </details>\n </li>\n </ol>\n","sidebarMacro":"JsSidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<p>\n The JavaScript exception \"is not a function\" occurs when there was an attempt to call a\n value from a function, but the value is not actually a function.\n</p>"}},{"type":"prose","value":{"id":"message","title":"Message","isH3":false,"content":"<pre class=\"brush: plain notranslate\">TypeError: \"x\" is not a function. (V8-based &amp; Firefox &amp; Safari)\n</pre>"}},{"type":"prose","value":{"id":"error_type","title":"Error type","isH3":false,"content":"<a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError\"><code>TypeError</code></a>"}},{"type":"prose","value":{"id":"what_went_wrong","title":"What went wrong?","isH3":false,"content":"<p>\n It attempted to call a value from a function, but the value is not actually a function.\n Some code expects you to provide a function, but that didn't happen.\n</p>\n<p>\n Maybe there is a typo in the function name? Maybe the object you are calling the method\n on does not have this function? For example, JavaScript <code>Objects</code> have no\n <code>map</code> function, but the JavaScript <code>Array</code> object does.\n</p>\n<p>\n There are many built-in functions in need of a (callback) function. You will have to\n provide a function in order to have these methods working properly:\n</p>\n<ul>\n <li>\n <p>When working with <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array\"><code>Array</code></a> or <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray\"><code>TypedArray</code></a> objects:</p>\n <ul>\n <li>\n <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every\"><code>Array.prototype.every()</code></a>, <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some\"><code>Array.prototype.some()</code></a>,\n <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach\"><code>Array.prototype.forEach()</code></a>, <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map\"><code>Array.prototype.map()</code></a>,\n <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter\"><code>Array.prototype.filter()</code></a>, <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce\"><code>Array.prototype.reduce()</code></a>,\n <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduceRight\"><code>Array.prototype.reduceRight()</code></a>, <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find\"><code>Array.prototype.find()</code></a>\n </li>\n </ul>\n </li>\n <li>\n <p>When working with <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map\"><code>Map</code></a> and <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set\"><code>Set</code></a> objects:</p>\n <ul>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/forEach\"><code>Map.prototype.forEach()</code></a> and <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/forEach\"><code>Set.prototype.forEach()</code></a></li>\n </ul>\n </li>\n</ul>"}},{"type":"prose","value":{"id":"examples","title":"Examples","isH3":false,"content":""}},{"type":"prose","value":{"id":"a_typo_in_the_function_name","title":"A typo in the function name","isH3":true,"content":"<p>In this case, which happens way too often, there is a typo in the method name:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-bad notranslate\"><code>const x = document.getElementByID(\"foo\");\n// TypeError: document.getElementByID is not a function\n</code></pre></div>\n<p>The correct function name is <code>getElementById</code>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-good notranslate\"><code>const x = document.getElementById(\"foo\");\n</code></pre></div>"}},{"type":"prose","value":{"id":"function_called_on_the_wrong_object","title":"Function called on the wrong object","isH3":true,"content":"<p>\n For certain methods, you have to provide a (callback) function and it will work on\n specific objects only. In this example, <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map\"><code>Array.prototype.map()</code></a> is used,\n which will work with <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array\"><code>Array</code></a> objects only.\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-bad notranslate\"><code>const obj = { a: 13, b: 37, c: 42 };\n\nobj.map(function (num) {\n return num * 2;\n});\n\n// TypeError: obj.map is not a function\n</code></pre></div>\n<p>Use an array instead:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-good notranslate\"><code>const numbers = [1, 4, 9];\n\nnumbers.map(function (num) {\n return num * 2;\n}); // [2, 8, 18]\n</code></pre></div>"}},{"type":"prose","value":{"id":"function_shares_a_name_with_a_pre-existing_property","title":"Function shares a name with a pre-existing property","isH3":true,"content":"<p>\n Sometimes when making a class, you may have a property and a function with the same\n name. Upon calling the function, the compiler thinks that the function ceases to exist.\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-bad notranslate\"><code>function Dog() {\n this.age = 11;\n this.color = \"black\";\n this.name = \"Ralph\";\n return this;\n}\n\nDog.prototype.name = function (name) {\n this.name = name;\n return this;\n};\n\nconst myNewDog = new Dog();\nmyNewDog.name(\"Cassidy\"); //Uncaught TypeError: myNewDog.name is not a function\n</code></pre></div>\n<p>Use a different property name instead:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-good notranslate\"><code>function Dog() {\n this.age = 11;\n this.color = \"black\";\n this.dogName = \"Ralph\"; //Using this.dogName instead of .name\n return this;\n}\n\nDog.prototype.name = function (name) {\n this.dogName = name;\n return this;\n};\n\nconst myNewDog = new Dog();\nmyNewDog.name(\"Cassidy\"); //Dog { age: 11, color: 'black', dogName: 'Cassidy' }\n</code></pre></div>"}},{"type":"prose","value":{"id":"using_parentheses_for_multiplication","title":"Using parentheses for multiplication","isH3":true,"content":"<p>In math, you can write 2 × (3 + 5) as 2*(3 + 5) or just 2(3 + 5).</p>\n<p>Using the latter will throw an error:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-bad notranslate\"><code>const sixteen = 2(3 + 5);\nconsole.log(`2 x (3 + 5) is ${sixteen}`);\n// Uncaught TypeError: 2 is not a function\n</code></pre></div>\n<p>You can correct the code by adding a <code>*</code> operator:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js example-good notranslate\"><code>const sixteen = 2 * (3 + 5);\nconsole.log(`2 x (3 + 5) is ${sixteen}`);\n// 2 x (3 + 5) is 16\n</code></pre></div>"}},{"type":"prose","value":{"id":"import_the_exported_module_correctly","title":"Import the exported module correctly","isH3":true,"content":"<p>Ensure you are importing the module correctly.</p>\n<p>An example helpers library (<code>helpers.js</code>)</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const helpers = function () {};\n\nhelpers.groupBy = function (objectArray, property) {\n return objectArray.reduce((acc, obj) =&gt; {\n const key = obj[property];\n acc[key] ??= [];\n acc[key].push(obj);\n return acc;\n }, {});\n};\n\nexport default helpers;\n</code></pre></div>\n<p>The correct import usage (<code>App.js</code>):</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>import helpers from \"./helpers\";\n</code></pre></div>"}},{"type":"prose","value":{"id":"see_also","title":"See also","isH3":false,"content":"<ul>\n <li><a href=\"/en-US/docs/Web/JavaScript/Reference/Functions\">Functions</a></li>\n</ul>"}}],"toc":[{"text":"Message","id":"message"},{"text":"Error type","id":"error_type"},{"text":"What went wrong?","id":"what_went_wrong"},{"text":"Examples","id":"examples"},{"text":"See also","id":"see_also"}],"summary":"The JavaScript exception \"is not a function\" occurs when there was an attempt to call a\n value from a function, but the value is not actually a function.","popularity":0.0098,"modified":"2024-09-23T14:02:45.000Z","other_translations":[{"locale":"de","title":"TypeError: \"x\" ist keine Funktion","native":"Deutsch"},{"locale":"es","title":"TypeError: \"x\" is not a function","native":"Español"},{"locale":"fr","title":"TypeError: \"x\" is not a function","native":"Français"},{"locale":"ja","title":"TypeError: \"x\" is not a function","native":"日本語"},{"locale":"pt-BR","title":"TypeError: \"x\" is not a function","native":"Português (do Brasil)"},{"locale":"ru","title":"TypeError: \"x\" is not a function","native":"Русский"},{"locale":"zh-CN","title":"TypeError: \"x\" is not a function","native":"中文 (简体)"},{"locale":"zh-TW","title":"TypeError: \"x\" is not a function","native":"正體中文 (繁體)"}],"pageType":"javascript-error","source":{"folder":"en-us/web/javascript/reference/errors/not_a_function","github_url":"https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/errors/not_a_function/index.md","last_commit_url":"https://github.com/mdn/content/commit/0a9c10fc67901972221dc7b3d006334fbfa73dce","filename":"index.md"},"short_title":"TypeError: \"x\" is not a function","parents":[{"uri":"/en-US/docs/Web","title":"References"},{"uri":"/en-US/docs/Web/JavaScript","title":"JavaScript"},{"uri":"/en-US/docs/Web/JavaScript/Reference","title":"Reference"},{"uri":"/en-US/docs/Web/JavaScript/Reference/Errors","title":"JavaScript error reference"},{"uri":"/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_function","title":"TypeError: \"x\" is not a function"}],"pageTitle":"TypeError: \"x\" is not a function - JavaScript | MDN","noIndexing":false}}</script></body></html>

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