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class="document-toc-link" href="#logging_levels_with_info_warn_and_error">Logging levels with info, warn, and error</a></li><li class="document-toc-item "><a class="document-toc-link" href="#displaying_tables_using_console.table">Displaying tables using <code>console.table()</code></a></li><li class="document-toc-item "><a class="document-toc-link" href="#counting_using_console.count">Counting using <code>console.count()</code></a></li><li class="document-toc-item "><a class="document-toc-link" href="#adding_timers_using_console.time_and_console.timer">Adding timers using <code>console.time()</code> and <code>console.timer()</code></a></li><li class="document-toc-item "><a class="document-toc-link" href="#grouping_logs_using_console.group">Grouping logs using <code>console.group()</code></a></li><li class="document-toc-item "><a class="document-toc-link" href="#creating_traces_using_console.trace">Creating traces using <code>console.trace()</code></a></li><li class="document-toc-item "><a class="document-toc-link" href="#cleaning_up_using_console.clear">Cleaning up using <code>console.clear()</code></a></li><li class="document-toc-item "><a class="document-toc-link" href="#summary">Summary</a></li></ul></section></div></nav></aside><section class="place side"></section></div><article class="blog-post blog-container main-page-content" lang="en-US"><figure class="blog-image"><img alt="Developer essentials: JavaScript console methods title. A vibrant gradient behind artwork of a terminal with some example commands and a keyboard." src="./console-logging-featured.png" height="420" width="800"/></figure><h1>Developer essentials: JavaScript console methods</h1><div class="date-author"><a href="https://bsmth.de" class="external author" target="_blank" rel="noreferrer"><img src="/en-US/blog/author/brian-smith/avatar.jpg" alt="Author avatar"/>Brian Smith</a><time class="date">November 30, 2023</time><span class="read-time">7 minute read</span></div><div class="section-content"><p> Building on our previous <a href="/en-US/blog/searching-code-with-grep/">"Developer essentials" post on grep</a>, we're looking at an API you'll always rely on when building for the web: the humble <a href="/en-US/docs/Web/API/console">console</a>. The console is where you experience delight when you see your JavaScript working, and sorrow when all you find is a cryptic error message. </p> <p> People use the console to log outputs such as a calculation's result, a REST API's return value, the outcome of string manipulation, a reminder to revisit a certain part of a program (e.g., <code>TODO: fix</code>). The possibilities are endless. You can use the console to output any kind of information you like. When running JavaScript in your browser, console logs are visible in your browser's developer console. </p> <p> In this article, we'll take a look at what the console can do and some of the lesser-known methods that you might find useful or just plain fun. Whether you're a beginner in web development, seeking to learn the purpose of the console, or an experienced developer, you might discover methods that you didn't know existed. Let's start off with the most common methods and then take a look at the others, with examples all along the way. </p></div><section aria-labelledby="logging_to_the_console"><h2 id="logging_to_the_console"><a href="#logging_to_the_console">Logging to the console</a></h2><div class="section-content"><p> If you know all about <a href="/en-US/docs/Web/API/console/log_static"><code>console.log()</code></a>, you can skip to <a href="#logging_levels_with_info_warn_and_error">logging levels</a> as we'll quickly cover the basics first. If you're still here, let's learn about what the console is and how it's used. Most people use <code>console.log()</code> to send generic information about their code to the console, which you can find in your browser's developer tools (e.g., <a href="https://firefox-source-docs.mozilla.org/devtools-user/" class="external" target="_blank">Firefox's Developer Tools</a>). </p> <div class="notecard note"> <p><strong>Note:</strong> You can copy and paste all of the examples below into your browser's console and try them out for yourself.</p> </div> <p>The <code>log()</code> method is the bread and butter of the console object: you provide something to <code>log()</code>, and voilà — it's logged to the console:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const hello = "Hi there, welcome to MDN Web Docs!"; console.log(hello); // Hi there, welcome to MDN Web Docs! </code></pre></div> <p>It's great to find out if your code is working as expected by making the output visible, like this example where I'm checking if I correctly used <a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat"><code>DateTimeFormat</code></a>:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const currentDate = new Date(); const formattedDate = new Intl.DateTimeFormat("en-US").format(currentDate); console.log("Current date:", formattedDate); // "Current date:" "11/28/2023" </code></pre></div> <p>You can provide multiple items in the log and apply some fancy formatting as well (for more details, see <a href="/en-US/docs/Web/API/console#outputting_text_to_the_console">Outputting text to the console</a>):</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const currentDate = new Date(); const formattedDate = new Intl.DateTimeFormat("en-US").format(currentDate); console.log("Today's date is %s", formattedDate); // Today's date is: 11/29/2023 </code></pre></div> <p> It's also fun to use the console interactively as most browsers support autocomplete that lets you tab through suggestions. If you don't know what to log, type <code>console.log(window.</code> (or any other object) and let browser suggest some interesting capabilities, like the <a href="/en-US/docs/Web/API/Window/navigator"><code>navigator</code></a>: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>console.log(window.navigator.oscpu); // Intel Mac OS X 10.15 </code></pre></div> <p>Don't forget to get rid of leftover <code>console.log()</code> calls in your code before you make it public, though! It's good practice to remove development logging from production applications.</p></div></section><section aria-labelledby="logging_levels_with_info_warn_and_error"><h2 id="logging_levels_with_info_warn_and_error"><a href="#logging_levels_with_info_warn_and_error">Logging levels with info, warn, and error</a></h2><div class="section-content"><p>You can add more meaningful logs with <code>info</code>, <code>warn</code>, and <code>error</code> levels by using <a href="/en-US/docs/Web/API/console/info_static"><code>console.info()</code></a>, <a href="/en-US/docs/Web/API/console/warn_static"><code>console.warn()</code></a>, and <a href="/en-US/docs/Web/API/console/error_static"><code>console.error()</code></a> methods.</p> <p> The effect is similar to <code>console.log()</code>, but the output is formatted differently (depending on the browser), and usually you can filter the output by logging level. This is useful if you only want to see errors, for example: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const browser = window.navigator.userAgent; console.info(browser); // Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:121.0) Gecko/20100101 Firefox/121.0 </code></pre></div> <p>If you know of cases where other people might run into trouble when running your code, <code>warn</code> and <code>error</code> messages are extremely helpful.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>console.warn("Unknown device - there may be compatibility issues."); // ⚠️ Unknown device - there may be compatibility issues. console.error("Unsupported device. See <docs url> for more details."); // 🛑 Unsupported device. See <docs url> for more details. // <stack trace> </code></pre></div> <p> Some browsers show a stack trace for <code>error</code> messages, but you can also call this feature directly using the console. We'll see how to do this later in this article in <a href="#creating_traces_using_console.trace">Creating traces using <code>console.trace()</code></a>. </p></div></section><section aria-labelledby="displaying_tables_using_console.table"><h2 id="displaying_tables_using_console.table"><a href="#displaying_tables_using_console.table">Displaying tables using <code>console.table()</code></a></h2><div class="section-content"><p> This is one of my favorite methods because I often find that I need to take the output of code, copy and paste it into an editor, and then spend some time formatting it to make it readable before I can understand what's happening. The amazing thing about the console is that you can create tables directly in the console using <a href="/en-US/docs/Web/API/console/table_static"><code>console.table()</code></a>. This makes perfect sense because usually you're running the code in the browser, and browsers can handle rendering tables pretty well already: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const dogs = [ { name: "Yoshi", color: "Black", personality: "Calm" }, { name: "Melanie", color: "Brown", personality: "Hyperactive" }, { name: "Peppers", color: "white", personality: "Unpredictable" }, ]; console.table(dogs); </code></pre></div> <p>Check out how this array looks when it's beautifully formatted as a table:</p> <p> <img src="console-table.png" alt="A JavaScript array formatted as an HTML table using the console.table() method. The data is a list of dogs along with their corresponding colors and personalities." loading="lazy"> </p></div></section><section aria-labelledby="counting_using_console.count"><h2 id="counting_using_console.count"><a href="#counting_using_console.count">Counting using <code>console.count()</code></a></h2><div class="section-content"><p> Why not add a counter to your logs to find out how often something happens? <a href="/en-US/docs/Web/API/console/count_static"><code>console.count()</code></a> is a great built-in method that you can use to count events away to your heart's content: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>function postBoostClicked() { // My post has been boosted, do something here console.count("Boost count"); } postBoostClicked(); // Boost count: 1 postBoostClicked(); // Boost count: 2 </code></pre></div></div></section><section aria-labelledby="adding_timers_using_console.time_and_console.timer"><h2 id="adding_timers_using_console.time_and_console.timer"><a href="#adding_timers_using_console.time_and_console.timer">Adding timers using <code>console.time()</code> and <code>console.timer()</code></a></h2><div class="section-content"><p> Two useful methods applicable in many situations are <a href="/en-US/docs/Web/API/console/time_static"><code>console.time()</code></a> and <a href="/en-US/docs/Web/API/console/timeend_static"><code>console.timeEnd()</code></a>, which start and stop a timer within your program. You can use these methods to measure how long something takes in your code, say you want to see how long it takes to execute a function. In this example, a function called <code>myFunction()</code> takes 200ms: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>console.time("timerName"); // call myFunction() console.timeEnd("timerName"); // timerName: 200ms - timer ended </code></pre></div> <p> If you find that you need to add some details with timing, you can also add notes using <a href="/en-US/docs/Web/API/console/timelog_static"><code>console.timeLog()</code></a>. This is useful if there are separate stages in your application like setting up different parts of the app: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>console.time("MyTimer"); console.timeLog("MyTimer", "Starting application up…"); // MyTimer: 0ms Starting application up… // call myFunction(), for example console.timeLog("MyTimer", "UI is setup, making API calls now"); // MyTimer: 200ms UI is setup, making API calls now // call otherFunction(), for example console.timeEnd("MyTimer"); // MyTimer: 300ms - timer ended </code></pre></div> <p>If you're interested in measuring your code beyond internal timers, you might want to look at the <a href="/en-US/docs/Web/API/Performance_API">Performance API</a>, which helps dig into application performance based on various standards and measurements.</p></div></section><section aria-labelledby="grouping_logs_using_console.group"><h2 id="grouping_logs_using_console.group"><a href="#grouping_logs_using_console.group">Grouping logs using <code>console.group()</code></a></h2><div class="section-content"><p> Grouping logs using <a href="/en-US/docs/Web/API/console/group_static"><code>console.group()</code></a> and <a href="/en-US/docs/Web/API/console/group_static"><code>console.groupCollapsed()</code></a> is a great way to organize the output if you're creating a lot of logs. If you have stages that your code goes through, like setup steps or different processing tasks, grouping logs can be very convenient. </p> <p>Groups are collapsible, meaning you can expand and collapse a group in the console if you want to show or hide logs, especially if there's a lot of information to sift through:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>console.group("Grouped Logs"); console.log("Log 1"); console.log("Log 2"); console.groupEnd(); // Grouped Logs // Log 1 // Log 2 console.groupCollapsed("Collapsed Group"); console.log("Log 3"); console.log("Log 4"); console.groupEnd(); // > Collapsed Group </code></pre></div></div></section><section aria-labelledby="creating_traces_using_console.trace"><h2 id="creating_traces_using_console.trace"><a href="#creating_traces_using_console.trace">Creating traces using <code>console.trace()</code></a></h2><div class="section-content"><p> This method is an excellent choice for situations where you need to explore how the code is behaving. When you use <a href="/en-US/docs/Web/API/console/trace_static"><code>console.trace()</code></a>, you're venturing into debugging territory and need to investigate where code is being executed. Tracing is very handy if there are complex conditions that are difficult to follow mentally just from reading the code. </p> <p> The following example shows how to add a trace to an example function (<code>example()</code>) to find out whether it's being called from <code>one()</code> or <code>two()</code>. There's a condition that flaps between <code>true</code> and <code>false</code> based on the time, so it's impossible to know whether <code>one()</code> or <code>two()</code> will call the function we're interested in: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>// Is the "currentSeconds" value odd or even? const currentSeconds = new Date().getSeconds(); const condition = currentSeconds % 2 === 0; function one() { example(); } function two() { example(); } function randomChoice() { if (!condition) { // OK, I'm lost! one(); } else { two(); } } function example() { // Where is this function called? console.trace("Trace from example() function"); } randomChoice(); // console.trace() Trace from example function // example debugger eval code:23 // one debugger eval code:6 // randomChoice debugger eval code:16 </code></pre></div> <p>From the trace, we can see that:</p> <ol> <li><code>trace</code> is executed inside <code>example()</code> on line 23</li> <li><code>example()</code> is called in the <code>one()</code> function on line 6</li> <li>The trace ends with the call of <code>randomChoice()</code> on line 16</li> </ol> <p>If you have code with complex logic or non-deterministic behavior, using <code>console.trace()</code> can be really helpful for working back through the stack and finding out the potential source of issues.</p></div></section><section aria-labelledby="cleaning_up_using_console.clear"><h2 id="cleaning_up_using_console.clear"><a href="#cleaning_up_using_console.clear">Cleaning up using <code>console.clear()</code></a></h2><div class="section-content"><p> Are you working with an application that logs too much information to the console for you to focus on a specific area or message? You can conveniently clear the console and restore it to a pristine condition using <a href="/en-US/docs/Web/API/console/clear_static"><code>console.clear()</code></a>: </p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>// Too much information! console.clear(); // Console was cleared. </code></pre></div> <p>The zen of an immaculate, clear console seems like a great place to conclude this article. So let's wrap it up here.</p></div></section><section aria-labelledby="summary"><h2 id="summary"><a href="#summary">Summary</a></h2><div class="section-content"><p> We've seen quite a few different ways of using the console in JavaScript. I hope you've learned something new, whether you're starting your web development journey or are an old <code>console.timer()</code>. If you think I've missed something worth mentioning, or if you have other feedback about this article, feel free to let us know on <a href="https://mozilla.social/@MDN" class="external" target="_blank">Mastodon</a> or <a href="/discord">Discord</a>. Thanks a lot for reading, and happy logging. 📒 </p></div></section><section class="previous-next"><a href="/en-US/blog/getting-started-with-css-container-queries/" class="previous"><article><h2><strong>Previous Post</strong> Getting started with CSS container queries</h2></article></a><a href="/en-US/blog/baseline-evolution-on-mdn/" class="next"><article><h2><strong>Next Post</strong> Baseline's evolution on MDN</h2></article></a></section></article><section class="section-newsletter"><h2>Stay Informed with MDN</h2><p>Get the MDN newsletter and never miss an update on the latest web development trends, tips, and best practices.</p><form class="mdn-form mdn-form-big"><div class="mdn-form-item"><label for="newsletter_email">Your email address:</label><input type="email" name="email" required="" placeholder="yourname@example.com" id="newsletter_email" value=""/></div><div class="mdn-form-item"><label for="newsletter_privacy"><input type="checkbox" id="newsletter_privacy" name="privacy" 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Content available under <a href="/en-US/docs/MDN/Writing_guidelines/Attrib_copyright_license">a Creative Commons license</a>.</p></div></div></footer></div><script type="application/json" id="hydration">{"url":"/en-US/blog/learn-javascript-console-methods/","blogMeta":{"slug":"learn-javascript-console-methods","title":"Developer essentials: JavaScript console methods","keywords":"javascript, reference, examples, console, browser","description":"The JavaScript console is an essential tool for web development. Learn new and fun ways to use the console to display data and debug your code.","image":{"file":"console-logging-featured.png","alt":"Developer essentials: JavaScript console methods title. A vibrant gradient behind artwork of a terminal with some example commands and a keyboard."},"sponsored":false,"date":"2023-11-30T00:00:00.000Z","author":{"name":"Brian Smith","link":"https://bsmth.de","avatar_url":"/en-US/blog/author/brian-smith/avatar.jpg"},"readTime":7,"links":{"previous":{"title":"Getting started with CSS container queries","slug":"getting-started-with-css-container-queries"},"next":{"title":"Baseline's evolution on MDN","slug":"baseline-evolution-on-mdn"}}},"doc":{"locale":"en-US","title":"Developer essentials: JavaScript console methods","mdn_url":"/en-US/blog/learn-javascript-console-methods/","native":"English (US)","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<p>\n Building on our previous <a href=\"/en-US/blog/searching-code-with-grep/\">\"Developer essentials\" post on grep</a>, we're looking at an API you'll always rely on when building for the web: the humble <a href=\"/en-US/docs/Web/API/console\">console</a>.\n The console is where you experience delight when you see your JavaScript working, and sorrow when all you find is a cryptic error message.\n</p>\n<p>\n People use the console to log outputs such as a calculation's result, a REST API's return value, the outcome of string manipulation, a reminder to revisit a certain part of a program (e.g., <code>TODO: fix</code>). The possibilities are endless.\n You can use the console to output any kind of information you like. When running JavaScript in your browser, console logs are visible in your browser's developer console.\n</p>\n<p>\n In this article, we'll take a look at what the console can do and some of the lesser-known methods that you might find useful or just plain fun.\n Whether you're a beginner in web development, seeking to learn the purpose of the console, or an experienced developer, you might discover methods that you didn't know existed.\n Let's start off with the most common methods and then take a look at the others, with examples all along the way.\n</p>"}},{"type":"prose","value":{"id":"logging_to_the_console","title":"Logging to the console","isH3":false,"content":"<p>\n If you know all about <a href=\"/en-US/docs/Web/API/console/log_static\"><code>console.log()</code></a>, you can skip to <a href=\"#logging_levels_with_info_warn_and_error\">logging levels</a> as we'll quickly cover the basics first.\n If you're still here, let's learn about what the console is and how it's used.\n Most people use <code>console.log()</code> to send generic information about their code to the console, which you can find in your browser's developer tools (e.g., <a href=\"https://firefox-source-docs.mozilla.org/devtools-user/\" class=\"external\" target=\"_blank\">Firefox's Developer Tools</a>).\n</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> You can copy and paste all of the examples below into your browser's console and try them out for yourself.</p>\n</div>\n<p>The <code>log()</code> method is the bread and butter of the console object: you provide something to <code>log()</code>, and voilà — it's logged to the console:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const hello = \"Hi there, welcome to MDN Web Docs!\";\nconsole.log(hello);\n// Hi there, welcome to MDN Web Docs!\n</code></pre></div>\n<p>It's great to find out if your code is working as expected by making the output visible, like this example where I'm checking if I correctly used <a href=\"/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat\"><code>DateTimeFormat</code></a>:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const currentDate = new Date();\nconst formattedDate = new Intl.DateTimeFormat(\"en-US\").format(currentDate);\nconsole.log(\"Current date:\", formattedDate);\n// \"Current date:\" \"11/28/2023\"\n</code></pre></div>\n<p>You can provide multiple items in the log and apply some fancy formatting as well (for more details, see <a href=\"/en-US/docs/Web/API/console#outputting_text_to_the_console\">Outputting text to the console</a>):</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const currentDate = new Date();\nconst formattedDate = new Intl.DateTimeFormat(\"en-US\").format(currentDate);\n\nconsole.log(\"Today's date is %s\", formattedDate);\n// Today's date is: 11/29/2023\n</code></pre></div>\n<p>\n It's also fun to use the console interactively as most browsers support autocomplete that lets you tab through suggestions.\n If you don't know what to log, type <code>console.log(window.</code> (or any other object) and let browser suggest some interesting capabilities, like the <a href=\"/en-US/docs/Web/API/Window/navigator\"><code>navigator</code></a>:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>console.log(window.navigator.oscpu);\n// Intel Mac OS X 10.15\n</code></pre></div>\n<p>Don't forget to get rid of leftover <code>console.log()</code> calls in your code before you make it public, though! It's good practice to remove development logging from production applications.</p>"}},{"type":"prose","value":{"id":"logging_levels_with_info_warn_and_error","title":"Logging levels with info, warn, and error","isH3":false,"content":"<p>You can add more meaningful logs with <code>info</code>, <code>warn</code>, and <code>error</code> levels by using <a href=\"/en-US/docs/Web/API/console/info_static\"><code>console.info()</code></a>, <a href=\"/en-US/docs/Web/API/console/warn_static\"><code>console.warn()</code></a>, and <a href=\"/en-US/docs/Web/API/console/error_static\"><code>console.error()</code></a> methods.</p>\n<p>\n The effect is similar to <code>console.log()</code>, but the output is formatted differently (depending on the browser), and usually you can filter the output by logging level.\n This is useful if you only want to see errors, for example:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const browser = window.navigator.userAgent;\nconsole.info(browser);\n// Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:121.0) Gecko/20100101 Firefox/121.0\n</code></pre></div>\n<p>If you know of cases where other people might run into trouble when running your code, <code>warn</code> and <code>error</code> messages are extremely helpful.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>console.warn(\"Unknown device - there may be compatibility issues.\");\n// ⚠️ Unknown device - there may be compatibility issues.\nconsole.error(\"Unsupported device. See <docs url> for more details.\");\n// 🛑 Unsupported device. See <docs url> for more details.\n// <stack trace>\n</code></pre></div>\n<p>\n Some browsers show a stack trace for <code>error</code> messages, but you can also call this feature directly using the console.\n We'll see how to do this later in this article in <a href=\"#creating_traces_using_console.trace\">Creating traces using <code>console.trace()</code></a>.\n</p>"}},{"type":"prose","value":{"id":"displaying_tables_using_console.table","title":"Displaying tables using <code>console.table()</code>","isH3":false,"content":"<p>\n This is one of my favorite methods because I often find that I need to take the output of code, copy and paste it into an editor, and then spend some time formatting it to make it readable before I can understand what's happening.\n The amazing thing about the console is that you can create tables directly in the console using <a href=\"/en-US/docs/Web/API/console/table_static\"><code>console.table()</code></a>.\n This makes perfect sense because usually you're running the code in the browser, and browsers can handle rendering tables pretty well already:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const dogs = [\n { name: \"Yoshi\", color: \"Black\", personality: \"Calm\" },\n { name: \"Melanie\", color: \"Brown\", personality: \"Hyperactive\" },\n { name: \"Peppers\", color: \"white\", personality: \"Unpredictable\" },\n];\n\nconsole.table(dogs);\n</code></pre></div>\n<p>Check out how this array looks when it's beautifully formatted as a table:</p>\n<p>\n <img src=\"console-table.png\" alt=\"A JavaScript array formatted as an HTML table using the console.table() method. The data is a list of dogs along with their corresponding colors and personalities.\" loading=\"lazy\">\n</p>"}},{"type":"prose","value":{"id":"counting_using_console.count","title":"Counting using <code>console.count()</code>","isH3":false,"content":"<p>\n Why not add a counter to your logs to find out how often something happens?\n <a href=\"/en-US/docs/Web/API/console/count_static\"><code>console.count()</code></a> is a great built-in method that you can use to count events away to your heart's content:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>function postBoostClicked() {\n // My post has been boosted, do something here\n console.count(\"Boost count\");\n}\n\npostBoostClicked();\n// Boost count: 1\npostBoostClicked();\n// Boost count: 2\n</code></pre></div>"}},{"type":"prose","value":{"id":"adding_timers_using_console.time_and_console.timer","title":"Adding timers using <code>console.time()</code> and <code>console.timer()</code>","isH3":false,"content":"<p>\n Two useful methods applicable in many situations are <a href=\"/en-US/docs/Web/API/console/time_static\"><code>console.time()</code></a> and <a href=\"/en-US/docs/Web/API/console/timeend_static\"><code>console.timeEnd()</code></a>, which start and stop a timer within your program.\n You can use these methods to measure how long something takes in your code, say you want to see how long it takes to execute a function.\n In this example, a function called <code>myFunction()</code> takes 200ms:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>console.time(\"timerName\");\n// call myFunction()\nconsole.timeEnd(\"timerName\");\n// timerName: 200ms - timer ended\n</code></pre></div>\n<p>\n If you find that you need to add some details with timing, you can also add notes using <a href=\"/en-US/docs/Web/API/console/timelog_static\"><code>console.timeLog()</code></a>.\n This is useful if there are separate stages in your application like setting up different parts of the app:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>console.time(\"MyTimer\");\nconsole.timeLog(\"MyTimer\", \"Starting application up…\");\n// MyTimer: 0ms Starting application up…\n// call myFunction(), for example\n\nconsole.timeLog(\"MyTimer\", \"UI is setup, making API calls now\");\n// MyTimer: 200ms UI is setup, making API calls now\n// call otherFunction(), for example\n\nconsole.timeEnd(\"MyTimer\");\n// MyTimer: 300ms - timer ended\n</code></pre></div>\n<p>If you're interested in measuring your code beyond internal timers, you might want to look at the <a href=\"/en-US/docs/Web/API/Performance_API\">Performance API</a>, which helps dig into application performance based on various standards and measurements.</p>"}},{"type":"prose","value":{"id":"grouping_logs_using_console.group","title":"Grouping logs using <code>console.group()</code>","isH3":false,"content":"<p>\n Grouping logs using <a href=\"/en-US/docs/Web/API/console/group_static\"><code>console.group()</code></a> and <a href=\"/en-US/docs/Web/API/console/group_static\"><code>console.groupCollapsed()</code></a> is a great way to organize the output if you're creating a lot of logs.\n If you have stages that your code goes through, like setup steps or different processing tasks, grouping logs can be very convenient.\n</p>\n<p>Groups are collapsible, meaning you can expand and collapse a group in the console if you want to show or hide logs, especially if there's a lot of information to sift through:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>console.group(\"Grouped Logs\");\nconsole.log(\"Log 1\");\nconsole.log(\"Log 2\");\nconsole.groupEnd();\n// Grouped Logs\n// Log 1\n// Log 2\n\nconsole.groupCollapsed(\"Collapsed Group\");\nconsole.log(\"Log 3\");\nconsole.log(\"Log 4\");\nconsole.groupEnd();\n// > Collapsed Group\n</code></pre></div>"}},{"type":"prose","value":{"id":"creating_traces_using_console.trace","title":"Creating traces using <code>console.trace()</code>","isH3":false,"content":"<p>\n This method is an excellent choice for situations where you need to explore how the code is behaving.\n When you use <a href=\"/en-US/docs/Web/API/console/trace_static\"><code>console.trace()</code></a>, you're venturing into debugging territory and need to investigate where code is being executed.\n Tracing is very handy if there are complex conditions that are difficult to follow mentally just from reading the code.\n</p>\n<p>\n The following example shows how to add a trace to an example function (<code>example()</code>) to find out whether it's being called from <code>one()</code> or <code>two()</code>.\n There's a condition that flaps between <code>true</code> and <code>false</code> based on the time, so it's impossible to know whether <code>one()</code> or <code>two()</code> will call the function we're interested in:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>// Is the \"currentSeconds\" value odd or even?\nconst currentSeconds = new Date().getSeconds();\nconst condition = currentSeconds % 2 === 0;\n\nfunction one() {\n example();\n}\nfunction two() {\n example();\n}\nfunction randomChoice() {\n if (!condition) {\n // OK, I'm lost!\n one();\n } else {\n two();\n }\n}\n\nfunction example() {\n // Where is this function called?\n console.trace(\"Trace from example() function\");\n}\n\nrandomChoice();\n// console.trace() Trace from example function\n// example debugger eval code:23\n// one debugger eval code:6\n// randomChoice debugger eval code:16\n</code></pre></div>\n<p>From the trace, we can see that:</p>\n<ol>\n <li><code>trace</code> is executed inside <code>example()</code> on line 23</li>\n <li><code>example()</code> is called in the <code>one()</code> function on line 6</li>\n <li>The trace ends with the call of <code>randomChoice()</code> on line 16</li>\n</ol>\n<p>If you have code with complex logic or non-deterministic behavior, using <code>console.trace()</code> can be really helpful for working back through the stack and finding out the potential source of issues.</p>"}},{"type":"prose","value":{"id":"cleaning_up_using_console.clear","title":"Cleaning up using <code>console.clear()</code>","isH3":false,"content":"<p>\n Are you working with an application that logs too much information to the console for you to focus on a specific area or message?\n You can conveniently clear the console and restore it to a pristine condition using <a href=\"/en-US/docs/Web/API/console/clear_static\"><code>console.clear()</code></a>:\n</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>// Too much information!\nconsole.clear();\n// Console was cleared.\n</code></pre></div>\n<p>The zen of an immaculate, clear console seems like a great place to conclude this article. So let's wrap it up here.</p>"}},{"type":"prose","value":{"id":"summary","title":"Summary","isH3":false,"content":"<p>\n We've seen quite a few different ways of using the console in JavaScript.\n I hope you've learned something new, whether you're starting your web development journey or are an old <code>console.timer()</code>.\n If you think I've missed something worth mentioning, or if you have other feedback about this article, feel free to let us know on <a href=\"https://mozilla.social/@MDN\" class=\"external\" target=\"_blank\">Mastodon</a> or <a href=\"/discord\">Discord</a>.\n Thanks a lot for reading, and happy logging. 📒\n</p>"}}],"pageTitle":"Developer essentials: JavaScript console methods | MDN Blog","noIndexing":false,"toc":[{"text":"Logging to the console","id":"logging_to_the_console"},{"text":"Logging levels with info, warn, and error","id":"logging_levels_with_info_warn_and_error"},{"text":"Displaying tables using <code>console.table()</code>","id":"displaying_tables_using_console.table"},{"text":"Counting using <code>console.count()</code>","id":"counting_using_console.count"},{"text":"Adding timers using <code>console.time()</code> and <code>console.timer()</code>","id":"adding_timers_using_console.time_and_console.timer"},{"text":"Grouping logs using <code>console.group()</code>","id":"grouping_logs_using_console.group"},{"text":"Creating traces using <code>console.trace()</code>","id":"creating_traces_using_console.trace"},{"text":"Cleaning up using <code>console.clear()</code>","id":"cleaning_up_using_console.clear"},{"text":"Summary","id":"summary"}],"summary":"The JavaScript console is an essential tool for web development. Learn new and fun ways to use the console to display data and debug your code."}}</script></body></html>