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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="#classes_and_constructors">Classes and constructors</a></li><li class="document-toc-item "><a class="document-toc-link" href="#inheritance">Inheritance</a></li><li class="document-toc-item "><a class="document-toc-link" href="#encapsulation">Encapsulation</a></li><li class="document-toc-item "><a class="document-toc-link" href="#test_your_skills!">Test your skills!</a></li><li class="document-toc-item "><a class="document-toc-link" href="#summary">Summary</a></li></ul></section></div></div><div class="sidebar-body"><ol><li class="section"><a href="/en-US/docs/Learn_web_development/Getting_started">Getting started modules</a></li><li 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href="/en-US/docs/Learn_web_development/Getting_started/Your_first_website/What_will_your_website_look_like">What will your website look like?</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Creating_the_content">HTML: Creating the content</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Styling_the_content">CSS: Styling the content</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Adding_interactivity">JavaScript: Adding interactivity</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Publishing_your_website">Publishing your website</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Getting_started/Web_standards">Web standards</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_the_web_works">How the web works</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Web_standards/The_web_standards_model">The web standards model</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_browsers_load_websites">How browsers load websites</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Getting_started/Soft_skills">Soft skills</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Research_and_learning">Research and learning</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Collaboration_and_teamwork">Collaboration and teamwork</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Workflows_and_processes">Workflows and processes</a></li><li><a href="/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Job_interviews">Succeeding in job interviews</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn_web_development/Core">Core modules</a></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Structuring_content">Structuring content with HTML</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Basic_HTML_syntax">Basic HTML syntax</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Webpage_metadata">What's in the head? Webpage metadata</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Headings_and_paragraphs">Headings and paragraphs in HTML</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Emphasis_and_importance">Emphasis and importance</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Lists">Lists</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_documents">Structuring documents</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Advanced_text_features">Advanced text features</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Creating_links">Creating links</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Marking_up_a_letter">Challenge: Marking up a letter</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_a_page_of_content">Challenge: Structuring a page of content</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_images">HTML images</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_video_and_audio">HTML video and audio</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Mozilla_splash_page">Challenge: Mozilla splash page</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_table_basics">HTML table basics</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Table_accessibility">HTML table accessibility</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Planet_data_table">Challenge: Structuring a planet data table</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms">Forms and buttons in HTML</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Structuring_content/Debugging_HTML">Debugging HTML</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Styling_basics">CSS styling basics</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/What_is_CSS">What is CSS?</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Getting_started">Getting started with CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Styling_a_bio_page">Challenge: Styling a biography page</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Basic_selectors">Basic CSS selectors</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Attribute_selectors">Attribute selectors</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Pseudo_classes_and_elements">Pseudo-classes and pseudo-elements</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Combinators">Combinators</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Box_model">The box model</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Handling_conflicts">Handling conflicts</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Values_and_units">CSS values and units</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Sizing">Sizing items in CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Backgrounds_and_borders">Backgrounds and borders</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Overflow">Overflowing content</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Images_media_forms">Images, media, and form elements</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Tables">Styling tables</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Debugging_CSS">Debugging CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Fundamental_CSS_comprehension">Challenge: Fundamental CSS comprehension</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Fancy_letterheaded_paper">Challenge: Creating fancy letterheaded paper</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box">Challenge: A cool-looking box</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Text_styling">CSS text styling</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Text_styling/Fundamentals">Fundamental text and font styling</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Text_styling/Styling_lists">Styling lists</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Text_styling/Styling_links">Styling links</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Text_styling/Web_fonts">Web fonts</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Text_styling/Typesetting_a_homepage">Challenge: Typesetting a community school homepage</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/CSS_layout">CSS layout</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Introduction">Introduction to CSS layout</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Floats">Floats</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Positioning">Positioning</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Flexbox">Flexbox</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Grids">CSS grid layout</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Responsive_Design">Responsive design</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Media_queries">Media query fundamentals</a></li><li><a href="/en-US/docs/Learn_web_development/Core/CSS_layout/Fundamental_Layout_Comprehension">Challenge: Fundamental layout comprehension</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Scripting">Dynamic scripting with JavaScript</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/What_is_JavaScript">What is JavaScript?</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/A_first_splash">A first splash into JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/What_went_wrong">What went wrong? Troubleshooting JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Variables">Storing the information you need — Variables</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Math">Basic math in JavaScript — numbers and operators</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Strings">Handling text — strings in JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Useful_string_methods">Useful string methods</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Arrays">Arrays</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator">Challenge: Silly story generator</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Conditionals">Making decisions in your code — conditionals</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Loops">Looping code</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Functions">Functions — reusable blocks of code</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Build_your_own_function">Build your own function</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Return_values">Function return values</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Events">Introduction to events</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Event_bubbling">Event bubbling</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Image_gallery">Challenge: Image gallery</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Object_basics">JavaScript object basics</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/DOM_scripting">DOM scripting introduction</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Network_requests">Making network requests with JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/JSON">Working with JSON</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Scripting/Debugging_JavaScript">Debugging JavaScript and handling errors</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries">JavaScript frameworks and libraries</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Introduction">Introduction to client-side frameworks</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Main_features">Framework main features</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_getting_started">Getting started with React</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_todo_list_beginning">Beginning our React todo list</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_components">Componentizing our React app</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_events_state">React interactivity: Events and state</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_filtering_conditional_rendering">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_accessibility">Accessibility in React</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_resources">React resources</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Core/Accessibility">Accessibility</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/What_is_accessibility">What is accessibility?</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/Tooling">Accessibility tooling and assistive technology</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/HTML">HTML: A good basis for accessibility</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/CSS_and_JavaScript">CSS and JavaScript accessibility best practices</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/WAI-ARIA_basics">WAI-ARIA basics</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/Multimedia">Accessible multimedia</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/Mobile">Mobile accessibility</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Accessibility/Accessibility_troubleshooting">Challenge: Accessibility troubleshooting</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/Core/Design_for_developers">Design for developers</a></li><li><a href="/en-US/docs/Learn_web_development/Core/Version_control">Version control</a></li><li class="section"><a href="/en-US/docs/Learn_web_development/Extensions">Extension modules</a></li><li class="toggle"><details open=""><summary><a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects">Advanced JavaScript objects</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_prototypes">Object prototypes</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming">Object-oriented programming</a></li><li><em><a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript" aria-current="page">Classes in JavaScript</a></em></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice">Object building practice</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Adding_bouncing_balls_features">Challenge: Adding features to our bouncing balls demo</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_APIs">Client-side web APIs</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Introduction">Introduction to web APIs</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Video_and_audio_APIs">Video and Audio APIs</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Drawing_graphics">Drawing graphics</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Client-side_storage">Client-side storage</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Third_party_APIs">Third-party APIs</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Async_JS">Asynchronous JavaScript</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Async_JS/Introducing">Introducing asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Async_JS/Promises">How to use promises</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Async_JS/Implementing_a_promise-based_API">How to implement a promise-based API</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Async_JS/Introducing_workers">Introducing workers</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Async_JS/Sequencing_animations">Challenge: Sequencing animations</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Forms">Web forms</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Your_first_form">Your first form</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/How_to_structure_a_web_form">How to structure a web form</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Basic_native_form_controls">Basic native form controls</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/HTML5_input_types">The HTML5 input types</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Other_form_controls">Other form controls</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Styling_web_forms">Styling web forms</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Advanced_form_styling">Advanced form styling</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/UI_pseudo-classes">UI pseudo-classes</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Form_validation">Client-side form validation</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Forms/Sending_and_retrieving_form_data">Sending form data</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_tools">Understanding client-side tools</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Overview">Client-side tooling overview</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Package_management">Package management basics</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Introducing_complete_toolchain">Introducing a complete toolchain</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Deployment">Deploying our app</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Server-side">Server-side websites</a></summary><ol><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps">Server-side first steps</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Introduction">Introduction to the server side</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Client-Server_overview">Client-Server Overview</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Web_frameworks">Server-side web frameworks</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Website_security">Website security</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django">Django web framework (Python)</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Introduction">Django introduction</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/development_environment">Setting up a Django development environment</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Tutorial_local_library_website">Django Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/skeleton_website">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Models">Django Tutorial Part 3: Using models</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Admin_site">Django Tutorial Part 4: Django admin site</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Home_page">Django Tutorial Part 5: Creating our home page</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Generic_views">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Sessions">Django Tutorial Part 7: Sessions framework</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Authentication">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Forms">Django Tutorial Part 9: Working with forms</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Testing">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Deployment">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/web_application_security">Django web application security</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Django/django_assessment_blog">Assessment: DIY Django mini blog</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs">Express web framework (Node.js)</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Introduction">Express/Node introduction</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/development_environment">Setting up a Node development environment</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Tutorial_local_library_website">Express Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/skeleton_website">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/mongoose">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/routes">Express Tutorial Part 4: Routes and controllers</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Displaying_data">Express Tutorial Part 5: Displaying library data</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/forms">Express Tutorial Part 6: Working with forms</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/deployment">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Performance">Web performance</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/why_web_performance">The "why" of web performance</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/What_is_web_performance">What is web performance?</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/Perceived_performance">Perceived performance</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/Measuring_performance">Measuring performance</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/Multimedia">Multimedia: Images</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/video">Multimedia: video</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/JavaScript">JavaScript performance optimization</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/HTML">HTML performance optimization</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/CSS">CSS performance optimization</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Performance/business_case_for_performance">The business case for web performance</a></li></ol></details></li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Extensions/Testing">Testing</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Introduction">Introduction to cross-browser testing</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Testing_strategies">Strategies for carrying out testing</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/HTML_and_CSS">Handling common HTML and CSS problems</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Feature_detection">Implementing feature detection</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Automated_testing">Introduction to automated testing</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Testing/Your_own_automation_environment">Setting up your own test automation environment</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Transform_animate">Transform and animate CSS</a></li><li><a href="/en-US/docs/Learn_web_development/Extensions/Security_privacy">Security and privacy</a></li><li class="section">Further resources</li><li class="toggle"><details><summary><a href="/en-US/docs/Learn_web_development/Howto">How to solve common problems</a></summary><ol><li><a href="/en-US/docs/Learn_web_development/Howto/Solve_HTML_problems">Solve common HTML problems</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Solve_CSS_problems">Solve common CSS problems</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Solve_JavaScript_problems">Solve common JavaScript problems</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Web_mechanics">Web mechanics</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Tools_and_setup">Tools and setup</a></li><li><a href="/en-US/docs/Learn_web_development/Howto/Design_and_accessibility">Design and accessibility</a></li></ol></details></li><li><a href="/en-US/docs/Learn_web_development/About">About</a></li><li><a href="/en-US/docs/Learn_web_development/Educators">Resources for educators</a></li><li><a href="/en-US/docs/Learn_web_development/Changelog">Changelog</a></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="#classes_and_constructors">Classes and constructors</a></li><li class="document-toc-item "><a class="document-toc-link" href="#inheritance">Inheritance</a></li><li class="document-toc-item "><a class="document-toc-link" href="#encapsulation">Encapsulation</a></li><li class="document-toc-item "><a class="document-toc-link" href="#test_your_skills!">Test your skills!</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></div><main id="content" class="main-content "><article class="main-page-content" lang="en-US"><header><h1>Classes in JavaScript</h1></header><div class="section-content"><ul class="prev-next"><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming"><span class="button-wrap"> Previous </span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects"><span class="button-wrap"> Overview: Advanced JavaScript objects</span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice"><span class="button-wrap"> Next </span></a></li></ul> <p>In the last article, we introduced some basic concepts of object-oriented programming (OOP), and discussed an example where we used OOP principles to model professors and students in a school.</p> <p>We also talked about how it's possible to use <a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_prototypes">prototypes</a> and <a href="/en-US/docs/Learn_web_development/Core/Scripting/Object_basics#introducing_constructors">constructors</a> to implement a model like this, and that JavaScript also provides features that map more closely to classical OOP concepts.</p> <p>In this article, we'll go through these features. It's worth keeping in mind that the features described here are not a new way of combining objects: under the hood, they still use prototypes. They're just a way to make it easier to set up a prototype chain.</p> <figure class="table-container"><table> <tbody> <tr> <th scope="row">Prerequisites:</th> <td> Familiarity with JavaScript basics (especially <a href="/en-US/docs/Learn_web_development/Core/Scripting/Object_basics">Object basics</a>) and object-oriented JavaScript concepts covered in previous lessons in this module. </td> </tr> <tr> <th scope="row">Learning outcomes:</th> <td> <ul> <li>Creating classes in JavaScript.</li> <li>Creating constructors in JavaScript.</li> <li>Inheritance and encapsulation in JavaScript.</li> </ul> </td> </tr> </tbody> </table></figure></div><section aria-labelledby="classes_and_constructors"><h2 id="classes_and_constructors"><a href="#classes_and_constructors">Classes and constructors</a></h2><div class="section-content"><p>You can declare a class using the <a href="/en-US/docs/Web/JavaScript/Reference/Statements/class"><code>class</code></a> keyword. Here's a class declaration for our <code>Person</code> from the previous article:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>class Person { name; constructor(name) { this.name = name; } introduceSelf() { console.log(`Hi! I'm ${this.name}`); } } </code></pre></div> <p>This declares a class called <code>Person</code>, with:</p> <ul> <li>a <code>name</code> property.</li> <li>a constructor that takes a <code>name</code> parameter that is used to initialize the new object's <code>name</code> property</li> <li>an <code>introduceSelf()</code> method that can refer to the object's properties using <code>this</code>.</li> </ul> <p>The <code>name;</code> declaration is optional: you could omit it, and the line <code>this.name = name;</code> in the constructor will create the <code>name</code> property before initializing it. However, listing properties explicitly in the class declaration might make it easier for people reading your code to see which properties are part of this class.</p> <p>You could also initialize the property to a default value when you declare it, with a line like <code>name = '';</code>.</p> <p>The constructor is defined using the <a href="/en-US/docs/Web/JavaScript/Reference/Classes/constructor"><code>constructor</code></a> keyword. Just like a <a href="/en-US/docs/Learn_web_development/Core/Scripting/Object_basics#introducing_constructors">constructor outside a class definition</a>, it will:</p> <ul> <li>create a new object</li> <li>bind <code>this</code> to the new object, so you can refer to <code>this</code> in your constructor code</li> <li>run the code in the constructor</li> <li>return the new object.</li> </ul> <p>Given the class declaration code above, you can create and use a new <code>Person</code> instance like this:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const giles = new Person("Giles"); giles.introduceSelf(); // Hi! I'm Giles </code></pre></div> <p>Note that we call the constructor using the name of the class, <code>Person</code> in this example.</p></div></section><section aria-labelledby="omitting_constructors"><h3 id="omitting_constructors"><a href="#omitting_constructors">Omitting constructors</a></h3><div class="section-content"><p>If you don't need to do any special initialization, you can omit the constructor, and a default constructor will be generated for you:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>class Animal { sleep() { console.log("zzzzzzz"); } } const spot = new Animal(); spot.sleep(); // 'zzzzzzz' </code></pre></div></div></section><section aria-labelledby="inheritance"><h2 id="inheritance"><a href="#inheritance">Inheritance</a></h2><div class="section-content"><p>Given our <code>Person</code> class above, let's define the <code>Professor</code> subclass.</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>class Professor extends Person { teaches; constructor(name, teaches) { super(name); this.teaches = teaches; } introduceSelf() { console.log( `My name is ${this.name}, and I will be your ${this.teaches} professor.`, ); } grade(paper) { const grade = Math.floor(Math.random() * (5 - 1) + 1); console.log(grade); } } </code></pre></div> <p>We use the <a href="/en-US/docs/Web/JavaScript/Reference/Classes/extends"><code>extends</code></a> keyword to say that this class inherits from another class.</p> <p>The <code>Professor</code> class adds a new property <code>teaches</code>, so we declare that.</p> <p>Since we want to set <code>teaches</code> when a new <code>Professor</code> is created, we define a constructor, which takes the <code>name</code> and <code>teaches</code> as arguments. The first thing this constructor does is call the superclass constructor using <a href="/en-US/docs/Web/JavaScript/Reference/Operators/super"><code>super()</code></a>, passing up the <code>name</code> parameter. The superclass constructor takes care of setting <code>name</code>. After that, the <code>Professor</code> constructor sets the <code>teaches</code> property.</p> <div class="notecard note"> <p><strong>Note:</strong> If a subclass has any of its own initialization to do, it <strong>must</strong> first call the superclass constructor using <code>super()</code>, passing up any parameters that the superclass constructor is expecting.</p> </div> <p>We've also overridden the <code>introduceSelf()</code> method from the superclass, and added a new method <code>grade()</code>, to grade a paper (our professor isn't very good, and just assigns random grades to papers).</p> <p>With this declaration we can now create and use professors:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const walsh = new Professor("Walsh", "Psychology"); walsh.introduceSelf(); // 'My name is Walsh, and I will be your Psychology professor' walsh.grade("my paper"); // some random grade </code></pre></div></div></section><section aria-labelledby="encapsulation"><h2 id="encapsulation"><a href="#encapsulation">Encapsulation</a></h2><div class="section-content"><p>Finally, let's see how to implement encapsulation in JavaScript. In the last article we discussed how we would like to make the <code>year</code> property of <code>Student</code> private, so we could change the rules about archery classes without breaking any code that uses the <code>Student</code> class.</p> <p>Here's a declaration of the <code>Student</code> class that does just that:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>class Student extends Person { #year; constructor(name, year) { super(name); this.#year = year; } introduceSelf() { console.log(`Hi! I'm ${this.name}, and I'm in year ${this.#year}.`); } canStudyArchery() { return this.#year > 1; } } </code></pre></div> <p>In this class declaration, <code>#year</code> is a <a href="/en-US/docs/Web/JavaScript/Reference/Classes/Private_properties">private data property</a>. We can construct a <code>Student</code> object, and it can use <code>#year</code> internally, but if code outside the object tries to access <code>#year</code> the browser throws an error:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>const summers = new Student("Summers", 2); summers.introduceSelf(); // Hi! I'm Summers, and I'm in year 2. summers.canStudyArchery(); // true summers.#year; // SyntaxError </code></pre></div> <div class="notecard note"> <p><strong>Note:</strong> Code run in the Chrome console can access private properties outside the class. This is a DevTools-only relaxation of the JavaScript syntax restriction.</p> </div> <p>Private data properties must be declared in the class declaration, and their names start with <code>#</code>.</p></div></section><section aria-labelledby="private_methods"><h3 id="private_methods"><a href="#private_methods">Private methods</a></h3><div class="section-content"><p>You can have private methods as well as private data properties. Just like private data properties, their names start with <code>#</code>, and they can only be called by the object's own methods:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>class Example { somePublicMethod() { this.#somePrivateMethod(); } #somePrivateMethod() { console.log("You called me?"); } } const myExample = new Example(); myExample.somePublicMethod(); // 'You called me?' myExample.#somePrivateMethod(); // SyntaxError </code></pre></div></div></section><section aria-labelledby="test_your_skills!"><h2 id="test_your_skills!"><a href="#test_your_skills!">Test your skills!</a></h2><div class="section-content"><p>You've reached the end of this article, but can you remember the most important information? You can find some further tests to verify that you've retained this information before you move on — see <a href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Test_your_skills:_Object-oriented_JavaScript">Test your skills: Object-oriented JavaScript</a>.</p></div></section><section aria-labelledby="summary"><h2 id="summary"><a href="#summary">Summary</a></h2><div class="section-content"><p>In this article, we've gone through the main tools available in JavaScript for writing object-oriented programs. We haven't covered everything here, but this should be enough to get you started. Our <a href="/en-US/docs/Web/JavaScript/Reference/Classes">article on Classes</a> is a good place to learn more.</p> <ul class="prev-next"><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming"><span class="button-wrap"> Previous </span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects"><span class="button-wrap"> Overview: Advanced JavaScript objects</span></a></li><li><a class="button secondary" href="/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice"><span class="button-wrap"> Next </span></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 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content are ©1998–2025 by individual mozilla.org contributors. 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/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript","doc":{"body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<ul class=\"prev-next\"><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming\"><span class=\"button-wrap\"> Previous </span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects\"><span class=\"button-wrap\"> Overview: Advanced JavaScript objects</span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice\"><span class=\"button-wrap\"> Next </span></a></li></ul>\n<p>In the last article, we introduced some basic concepts of object-oriented programming (OOP), and discussed an example where we used OOP principles to model professors and students in a school.</p>\n<p>We also talked about how it's possible to use <a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_prototypes\">prototypes</a> and <a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Object_basics#introducing_constructors\">constructors</a> to implement a model like this, and that JavaScript also provides features that map more closely to classical OOP concepts.</p>\n<p>In this article, we'll go through these features. It's worth keeping in mind that the features described here are not a new way of combining objects: under the hood, they still use prototypes. They're just a way to make it easier to set up a prototype chain.</p>\n<figure class=\"table-container\"><table>\n <tbody>\n <tr>\n <th scope=\"row\">Prerequisites:</th>\n <td>\n Familiarity with JavaScript basics\n (especially\n <a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Object_basics\">Object basics</a>) and object-oriented JavaScript concepts covered in previous lessons in this module.\n </td>\n </tr>\n <tr>\n <th scope=\"row\">Learning outcomes:</th>\n <td>\n <ul>\n <li>Creating classes in JavaScript.</li>\n <li>Creating constructors in JavaScript.</li>\n <li>Inheritance and encapsulation in JavaScript.</li>\n </ul>\n </td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"classes_and_constructors","title":"Classes and constructors","isH3":false,"content":"<p>You can declare a class using the <a href=\"/en-US/docs/Web/JavaScript/Reference/Statements/class\"><code>class</code></a> keyword. Here's a class declaration for our <code>Person</code> from the previous article:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>class Person {\n name;\n\n constructor(name) {\n this.name = name;\n }\n\n introduceSelf() {\n console.log(`Hi! I'm ${this.name}`);\n }\n}\n</code></pre></div>\n<p>This declares a class called <code>Person</code>, with:</p>\n<ul>\n<li>a <code>name</code> property.</li>\n<li>a constructor that takes a <code>name</code> parameter that is used to initialize the new object's <code>name</code> property</li>\n<li>an <code>introduceSelf()</code> method that can refer to the object's properties using <code>this</code>.</li>\n</ul>\n<p>The <code>name;</code> declaration is optional: you could omit it, and the line <code>this.name = name;</code> in the constructor will create the <code>name</code> property before initializing it. However, listing properties explicitly in the class declaration might make it easier for people reading your code to see which properties are part of this class.</p>\n<p>You could also initialize the property to a default value when you declare it, with a line like <code>name = '';</code>.</p>\n<p>The constructor is defined using the <a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/constructor\"><code>constructor</code></a> keyword. Just like a <a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Object_basics#introducing_constructors\">constructor outside a class definition</a>, it will:</p>\n<ul>\n<li>create a new object</li>\n<li>bind <code>this</code> to the new object, so you can refer to <code>this</code> in your constructor code</li>\n<li>run the code in the constructor</li>\n<li>return the new object.</li>\n</ul>\n<p>Given the class declaration code above, you can create and use a new <code>Person</code> instance like this:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const giles = new Person(\"Giles\");\n\ngiles.introduceSelf(); // Hi! I'm Giles\n</code></pre></div>\n<p>Note that we call the constructor using the name of the class, <code>Person</code> in this example.</p>"}},{"type":"prose","value":{"id":"omitting_constructors","title":"Omitting constructors","isH3":true,"content":"<p>If you don't need to do any special initialization, you can omit the constructor, and a default constructor will be generated for you:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>class Animal {\n sleep() {\n console.log(\"zzzzzzz\");\n }\n}\n\nconst spot = new Animal();\n\nspot.sleep(); // 'zzzzzzz'\n</code></pre></div>"}},{"type":"prose","value":{"id":"inheritance","title":"Inheritance","isH3":false,"content":"<p>Given our <code>Person</code> class above, let's define the <code>Professor</code> subclass.</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>class Professor extends Person {\n teaches;\n\n constructor(name, teaches) {\n super(name);\n this.teaches = teaches;\n }\n\n introduceSelf() {\n console.log(\n `My name is ${this.name}, and I will be your ${this.teaches} professor.`,\n );\n }\n\n grade(paper) {\n const grade = Math.floor(Math.random() * (5 - 1) + 1);\n console.log(grade);\n }\n}\n</code></pre></div>\n<p>We use the <a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/extends\"><code>extends</code></a> keyword to say that this class inherits from another class.</p>\n<p>The <code>Professor</code> class adds a new property <code>teaches</code>, so we declare that.</p>\n<p>Since we want to set <code>teaches</code> when a new <code>Professor</code> is created, we define a constructor, which takes the <code>name</code> and <code>teaches</code> as arguments. The first thing this constructor does is call the superclass constructor using <a href=\"/en-US/docs/Web/JavaScript/Reference/Operators/super\"><code>super()</code></a>, passing up the <code>name</code> parameter. The superclass constructor takes care of setting <code>name</code>. After that, the <code>Professor</code> constructor sets the <code>teaches</code> property.</p>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nIf a subclass has any of its own initialization to do, it <strong>must</strong> first call the superclass constructor using <code>super()</code>, passing up any parameters that the superclass constructor is expecting.</p>\n</div>\n<p>We've also overridden the <code>introduceSelf()</code> method from the superclass, and added a new method <code>grade()</code>, to grade a paper (our professor isn't very good, and just assigns random grades to papers).</p>\n<p>With this declaration we can now create and use professors:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const walsh = new Professor(\"Walsh\", \"Psychology\");\nwalsh.introduceSelf(); // 'My name is Walsh, and I will be your Psychology professor'\n\nwalsh.grade(\"my paper\"); // some random grade\n</code></pre></div>"}},{"type":"prose","value":{"id":"encapsulation","title":"Encapsulation","isH3":false,"content":"<p>Finally, let's see how to implement encapsulation in JavaScript. In the last article we discussed how we would like to make the <code>year</code> property of <code>Student</code> private, so we could change the rules about archery classes without breaking any code that uses the <code>Student</code> class.</p>\n<p>Here's a declaration of the <code>Student</code> class that does just that:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>class Student extends Person {\n #year;\n\n constructor(name, year) {\n super(name);\n this.#year = year;\n }\n\n introduceSelf() {\n console.log(`Hi! I'm ${this.name}, and I'm in year ${this.#year}.`);\n }\n\n canStudyArchery() {\n return this.#year > 1;\n }\n}\n</code></pre></div>\n<p>In this class declaration, <code>#year</code> is a <a href=\"/en-US/docs/Web/JavaScript/Reference/Classes/Private_properties\">private data property</a>. We can construct a <code>Student</code> object, and it can use <code>#year</code> internally, but if code outside the object tries to access <code>#year</code> the browser throws an error:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>const summers = new Student(\"Summers\", 2);\n\nsummers.introduceSelf(); // Hi! I'm Summers, and I'm in year 2.\nsummers.canStudyArchery(); // true\n\nsummers.#year; // SyntaxError\n</code></pre></div>\n<div class=\"notecard note\">\n<p><strong>Note:</strong>\nCode run in the Chrome console can access private properties outside the class. This is a DevTools-only relaxation of the JavaScript syntax restriction.</p>\n</div>\n<p>Private data properties must be declared in the class declaration, and their names start with <code>#</code>.</p>"}},{"type":"prose","value":{"id":"private_methods","title":"Private methods","isH3":true,"content":"<p>You can have private methods as well as private data properties. Just like private data properties, their names start with <code>#</code>, and they can only be called by the object's own methods:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>class Example {\n somePublicMethod() {\n this.#somePrivateMethod();\n }\n\n #somePrivateMethod() {\n console.log(\"You called me?\");\n }\n}\n\nconst myExample = new Example();\n\nmyExample.somePublicMethod(); // 'You called me?'\n\nmyExample.#somePrivateMethod(); // SyntaxError\n</code></pre></div>"}},{"type":"prose","value":{"id":"test_your_skills!","title":"Test your skills!","isH3":false,"content":"<p>You've reached the end of this article, but can you remember the most important information? You can find some further tests to verify that you've retained this information before you move on — see <a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Test_your_skills:_Object-oriented_JavaScript\">Test your skills: Object-oriented JavaScript</a>.</p>"}},{"type":"prose","value":{"id":"summary","title":"Summary","isH3":false,"content":"<p>In this article, we've gone through the main tools available in JavaScript for writing object-oriented programs. We haven't covered everything here, but this should be enough to get you started. Our <a href=\"/en-US/docs/Web/JavaScript/Reference/Classes\">article on Classes</a> is a good place to learn more.</p>\n<ul class=\"prev-next\"><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming\"><span class=\"button-wrap\"> Previous </span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects\"><span class=\"button-wrap\"> Overview: Advanced JavaScript objects</span></a></li><li><a class=\"button secondary\" href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice\"><span class=\"button-wrap\"> Next </span></a></li></ul>"}}],"isActive":true,"isMarkdown":true,"isTranslated":false,"locale":"en-US","mdn_url":"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript","modified":"2024-12-19T15:37:45.000Z","native":"English (US)","noIndexing":false,"other_translations":[{"locale":"de","title":"Klassen in JavaScript","native":"Deutsch"},{"locale":"es","title":"Clases en JavaScript","native":"Español"},{"locale":"fr","title":"L'héritage au sein de JavaScript","native":"Français"},{"locale":"ja","title":"JavaScript のクラス","native":"日本語"},{"locale":"ko","title":"Classes in JavaScript","native":"한국어"},{"locale":"pt-BR","title":"Herança em JavaScript","native":"Português (do Brasil)"},{"locale":"ru","title":"Наследование в JavaScript","native":"Русский"},{"locale":"zh-CN","title":"JavaScript 中的类","native":"中文 (简体)"},{"locale":"zh-TW","title":"JavaScript 中的「繼承」","native":"正體中文 (繁體)"}],"pageTitle":"Classes in JavaScript - Learn web development | MDN","parents":[{"uri":"/en-US/docs/Learn_web_development","title":"Learn"},{"uri":"/en-US/docs/Learn_web_development/Extensions","title":"Extension modules"},{"uri":"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects","title":"Advanced JavaScript objects"},{"uri":"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript","title":"Classes in JavaScript"}],"popularity":null,"short_title":"Classes in JavaScript","sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Getting_started\">Getting started modules</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup\">Environment setup</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Installing_software\">Installing basic software</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Browsing_the_web\">Browsing the web</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Code_editors\">Code editors</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Dealing_with_files\">Dealing with files</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Environment_setup/Command_line\">Command line crash course</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website\">Your first website</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/What_will_your_website_look_like\">What will your website look like?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Creating_the_content\">HTML: Creating the content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Styling_the_content\">CSS: Styling the content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Adding_interactivity\">JavaScript: Adding interactivity</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Your_first_website/Publishing_your_website\">Publishing your website</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards\">Web standards</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_the_web_works\">How the web works</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/The_web_standards_model\">The web standards model</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Web_standards/How_browsers_load_websites\">How browsers load websites</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills\">Soft skills</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Research_and_learning\">Research and learning</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Collaboration_and_teamwork\">Collaboration and teamwork</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Workflows_and_processes\">Workflows and processes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Getting_started/Soft_skills/Job_interviews\">Succeeding in job interviews</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Core\">Core modules</a></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content\">Structuring content with HTML</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Basic_HTML_syntax\">Basic HTML syntax</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Webpage_metadata\">What's in the head? Webpage metadata</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Headings_and_paragraphs\">Headings and paragraphs in HTML</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Emphasis_and_importance\">Emphasis and importance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Lists\">Lists</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_documents\">Structuring documents</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Advanced_text_features\">Advanced text features</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Creating_links\">Creating links</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Marking_up_a_letter\">Challenge: Marking up a letter</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Structuring_a_page_of_content\">Challenge: Structuring a page of content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_images\">HTML images</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_video_and_audio\">HTML video and audio</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Mozilla_splash_page\">Challenge: Mozilla splash page</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_table_basics\">HTML table basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Table_accessibility\">HTML table accessibility</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Planet_data_table\">Challenge: Structuring a planet data table</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms\">Forms and buttons in HTML</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Structuring_content/Debugging_HTML\">Debugging HTML</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics\">CSS styling basics</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/What_is_CSS\">What is CSS?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Getting_started\">Getting started with CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Styling_a_bio_page\">Challenge: Styling a biography page</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Basic_selectors\">Basic CSS selectors</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Attribute_selectors\">Attribute selectors</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Pseudo_classes_and_elements\">Pseudo-classes and pseudo-elements</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Combinators\">Combinators</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Box_model\">The box model</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Handling_conflicts\">Handling conflicts</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Values_and_units\">CSS values and units</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Sizing\">Sizing items in CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Backgrounds_and_borders\">Backgrounds and borders</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Overflow\">Overflowing content</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Images_media_forms\">Images, media, and form elements</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Tables\">Styling tables</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Debugging_CSS\">Debugging CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Fundamental_CSS_comprehension\">Challenge: Fundamental CSS comprehension</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Fancy_letterheaded_paper\">Challenge: Creating fancy letterheaded paper</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box\">Challenge: A cool-looking box</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling\">CSS text styling</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Fundamentals\">Fundamental text and font styling</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Styling_lists\">Styling lists</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Styling_links\">Styling links</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Web_fonts\">Web fonts</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Text_styling/Typesetting_a_homepage\">Challenge: Typesetting a community school homepage</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout\">CSS layout</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Introduction\">Introduction to CSS layout</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Floats\">Floats</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Positioning\">Positioning</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Flexbox\">Flexbox</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Grids\">CSS grid layout</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Responsive_Design\">Responsive design</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Media_queries\">Media query fundamentals</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/CSS_layout/Fundamental_Layout_Comprehension\">Challenge: Fundamental layout comprehension</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Scripting\">Dynamic scripting with JavaScript</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/What_is_JavaScript\">What is JavaScript?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/A_first_splash\">A first splash into JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/What_went_wrong\">What went wrong? Troubleshooting JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Variables\">Storing the information you need — Variables</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Math\">Basic math in JavaScript — numbers and operators</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Strings\">Handling text — strings in JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Useful_string_methods\">Useful string methods</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Arrays\">Arrays</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Silly_story_generator\">Challenge: Silly story generator</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Conditionals\">Making decisions in your code — conditionals</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Loops\">Looping code</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Functions\">Functions — reusable blocks of code</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Build_your_own_function\">Build your own function</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Return_values\">Function return values</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Events\">Introduction to events</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Event_bubbling\">Event bubbling</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Image_gallery\">Challenge: Image gallery</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Object_basics\">JavaScript object basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/DOM_scripting\">DOM scripting introduction</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Network_requests\">Making network requests with JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/JSON\">Working with JSON</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Scripting/Debugging_JavaScript\">Debugging JavaScript and handling errors</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries\">JavaScript frameworks and libraries</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Introduction\">Introduction to client-side frameworks</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/Main_features\">Framework main features</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_getting_started\">Getting started with React</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_todo_list_beginning\">Beginning our React todo list</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_components\">Componentizing our React app</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_events_state\">React interactivity: Events and state</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_interactivity_filtering_conditional_rendering\">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_accessibility\">Accessibility in React</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Frameworks_libraries/React_resources\">React resources</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility\">Accessibility</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/What_is_accessibility\">What is accessibility?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Tooling\">Accessibility tooling and assistive technology</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/HTML\">HTML: A good basis for accessibility</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/CSS_and_JavaScript\">CSS and JavaScript accessibility best practices</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/WAI-ARIA_basics\">WAI-ARIA basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Multimedia\">Accessible multimedia</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Mobile\">Mobile accessibility</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Accessibility/Accessibility_troubleshooting\">Challenge: Accessibility troubleshooting</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Design_for_developers\">Design for developers</a></li><li><a href=\"/en-US/docs/Learn_web_development/Core/Version_control\">Version control</a></li><li class=\"section\"><a href=\"/en-US/docs/Learn_web_development/Extensions\">Extension modules</a></li><li class=\"toggle\"><details open=\"\"><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects\">Advanced JavaScript objects</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_prototypes\">Object prototypes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object-oriented_programming\">Object-oriented programming</a></li><li><em><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Classes_in_JavaScript\" aria-current=\"page\">Classes in JavaScript</a></em></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Object_building_practice\">Object building practice</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Advanced_JavaScript_objects/Adding_bouncing_balls_features\">Challenge: Adding features to our bouncing balls demo</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs\">Client-side web APIs</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Introduction\">Introduction to web APIs</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Video_and_audio_APIs\">Video and Audio APIs</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Drawing_graphics\">Drawing graphics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Client-side_storage\">Client-side storage</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_APIs/Third_party_APIs\">Third-party APIs</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS\">Asynchronous JavaScript</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Introducing\">Introducing asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Promises\">How to use promises</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Implementing_a_promise-based_API\">How to implement a promise-based API</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Introducing_workers\">Introducing workers</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Async_JS/Sequencing_animations\">Challenge: Sequencing animations</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms\">Web forms</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Your_first_form\">Your first form</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/How_to_structure_a_web_form\">How to structure a web form</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Basic_native_form_controls\">Basic native form controls</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/HTML5_input_types\">The HTML5 input types</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Other_form_controls\">Other form controls</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Styling_web_forms\">Styling web forms</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Advanced_form_styling\">Advanced form styling</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/UI_pseudo-classes\">UI pseudo-classes</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Form_validation\">Client-side form validation</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Forms/Sending_and_retrieving_form_data\">Sending form data</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools\">Understanding client-side tools</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Overview\">Client-side tooling overview</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Package_management\">Package management basics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Introducing_complete_toolchain\">Introducing a complete toolchain</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Client-side_tools/Deployment\">Deploying our app</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side\">Server-side websites</a></summary><ol><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps\">Server-side first steps</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Introduction\">Introduction to the server side</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Client-Server_overview\">Client-Server Overview</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Web_frameworks\">Server-side web frameworks</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/First_steps/Website_security\">Website security</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django\">Django web framework (Python)</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Introduction\">Django introduction</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/development_environment\">Setting up a Django development environment</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Tutorial_local_library_website\">Django Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/skeleton_website\">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Models\">Django Tutorial Part 3: Using models</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Admin_site\">Django Tutorial Part 4: Django admin site</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Home_page\">Django Tutorial Part 5: Creating our home page</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Generic_views\">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Sessions\">Django Tutorial Part 7: Sessions framework</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Authentication\">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Forms\">Django Tutorial Part 9: Working with forms</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Testing\">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/Deployment\">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/web_application_security\">Django web application security</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Django/django_assessment_blog\">Assessment: DIY Django mini blog</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs\">Express web framework (Node.js)</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Introduction\">Express/Node introduction</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/development_environment\">Setting up a Node development environment</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Tutorial_local_library_website\">Express Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/skeleton_website\">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/mongoose\">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/routes\">Express Tutorial Part 4: Routes and controllers</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/Displaying_data\">Express Tutorial Part 5: Displaying library data</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/forms\">Express Tutorial Part 6: Working with forms</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Server-side/Express_Nodejs/deployment\">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance\">Web performance</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/why_web_performance\">The \"why\" of web performance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/What_is_web_performance\">What is web performance?</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/Perceived_performance\">Perceived performance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/Measuring_performance\">Measuring performance</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/Multimedia\">Multimedia: Images</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/video\">Multimedia: video</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/JavaScript\">JavaScript performance optimization</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/HTML\">HTML performance optimization</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/CSS\">CSS performance optimization</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Performance/business_case_for_performance\">The business case for web performance</a></li></ol></details></li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing\">Testing</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Introduction\">Introduction to cross-browser testing</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Testing_strategies\">Strategies for carrying out testing</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/HTML_and_CSS\">Handling common HTML and CSS problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Feature_detection\">Implementing feature detection</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Automated_testing\">Introduction to automated testing</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Testing/Your_own_automation_environment\">Setting up your own test automation environment</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Transform_animate\">Transform and animate CSS</a></li><li><a href=\"/en-US/docs/Learn_web_development/Extensions/Security_privacy\">Security and privacy</a></li><li class=\"section\">Further resources</li><li class=\"toggle\"><details><summary><a href=\"/en-US/docs/Learn_web_development/Howto\">How to solve common problems</a></summary><ol><li><a href=\"/en-US/docs/Learn_web_development/Howto/Solve_HTML_problems\">Solve common HTML problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Solve_CSS_problems\">Solve common CSS problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Solve_JavaScript_problems\">Solve common JavaScript problems</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Web_mechanics\">Web mechanics</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Tools_and_setup\">Tools and setup</a></li><li><a href=\"/en-US/docs/Learn_web_development/Howto/Design_and_accessibility\">Design and accessibility</a></li></ol></details></li><li><a href=\"/en-US/docs/Learn_web_development/About\">About</a></li><li><a href=\"/en-US/docs/Learn_web_development/Educators\">Resources for educators</a></li><li><a href=\"/en-US/docs/Learn_web_development/Changelog\">Changelog</a></li></ol>","source":{"folder":"en-us/learn_web_development/extensions/advanced_javascript_objects/classes_in_javascript","github_url":"https://github.com/mdn/content/blob/main/files/en-us/learn_web_development/extensions/advanced_javascript_objects/classes_in_javascript/index.md","last_commit_url":"https://github.com/mdn/content/commit/5b20f5f4265f988f80f513db0e4b35c7e0cd70dc","filename":"index.md"},"summary":"In the last article, we introduced some basic concepts of object-oriented programming (OOP), and discussed an example where we used OOP principles to model professors and students in a school.","title":"Classes in JavaScript","toc":[{"text":"Classes and constructors","id":"classes_and_constructors"},{"text":"Inheritance","id":"inheritance"},{"text":"Encapsulation","id":"encapsulation"},{"text":"Test your skills!","id":"test_your_skills!"},{"text":"Summary","id":"summary"}],"pageType":"learn-module-chapter"}}</script></body></html>