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Metadata in HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals">HTML text fundamentals</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks">Creating hyperlinks</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Advanced_text_formatting">Advanced text formatting</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure">Document and website structure</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML">Debugging HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter">Marking up a letter</a></li><li><a href="/en-US/docs/Learn/HTML/Introduction_to_HTML/Structuring_a_page_of_content">Structuring a page of content</a></li></ol></details></li><li><details><summary>Multimedia and embedding</summary><ol><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding">Multimedia and embedding</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Images_in_HTML">Images in HTML</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Video_and_audio_content">Video and audio content</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Other_embedding_technologies">From object to iframe — other embedding technologies</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Adding_vector_graphics_to_the_Web">Adding vector graphics to the web</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images">Responsive images</a></li><li><a href="/en-US/docs/Learn/HTML/Multimedia_and_embedding/Mozilla_splash_page">Mozilla splash page</a></li></ol></details></li><li><details><summary>HTML tables</summary><ol><li><a href="/en-US/docs/Learn/HTML/Tables">HTML tables</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Basics">HTML table basics</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Advanced">HTML table advanced features and accessibility</a></li><li><a href="/en-US/docs/Learn/HTML/Tables/Structuring_planet_data">Structuring planet data</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/CSS">CSS — Styling the web</a></li><li><details><summary>CSS first steps</summary><ol><li><a href="/en-US/docs/Learn/CSS/First_steps">CSS first steps</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/What_is_CSS">What is CSS?</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/Getting_started">Getting started with CSS</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/How_CSS_is_structured">How CSS is structured</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/How_CSS_works">How CSS works</a></li><li><a href="/en-US/docs/Learn/CSS/First_steps/Styling_a_biography_page">Styling a biography page</a></li></ol></details></li><li><details><summary>CSS building blocks</summary><ol><li><a href="/en-US/docs/Learn/CSS/Building_blocks">CSS building blocks</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors">CSS selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Type_Class_and_ID_Selectors">Type, class, and ID selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Attribute_selectors">Attribute selectors</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements">Pseudo-classes and pseudo-elements</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators">Combinators</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance">Cascade, specificity, and inheritance</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Cascade_layers">Cascade layers</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/The_box_model">The box model</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Backgrounds_and_borders">Backgrounds and borders</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Handling_different_text_directions">Handling different text directions</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Overflowing_content">Overflowing content</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Values_and_units">CSS values and units</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Sizing_items_in_CSS">Sizing items in CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Images_media_form_elements">Images, media, and form elements</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Styling_tables">Styling tables</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Advanced_styling_effects">Advanced styling effects</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Debugging_CSS">Debugging CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Organizing">Organizing your CSS</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Fundamental_CSS_comprehension">Fundamental CSS comprehension</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/Creating_fancy_letterheaded_paper">Creating fancy letterheaded paper</a></li><li><a href="/en-US/docs/Learn/CSS/Building_blocks/A_cool_looking_box">A cool-looking box</a></li></ol></details></li><li><details><summary>Styling text</summary><ol><li><a href="/en-US/docs/Learn/CSS/Styling_text">CSS styling text</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Fundamentals">Fundamental text and font styling</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Styling_lists">Styling lists</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Styling_links">Styling links</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Web_fonts">Web fonts</a></li><li><a href="/en-US/docs/Learn/CSS/Styling_text/Typesetting_a_homepage">Typesetting a community school homepage</a></li></ol></details></li><li><details><summary>CSS layout</summary><ol><li><a href="/en-US/docs/Learn/CSS/CSS_layout">CSS layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Introduction">Introduction to CSS layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Normal_Flow">Normal Flow</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Flexbox">Flexbox</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Grids">Grids</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Floats">Floats</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Positioning">Positioning</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Multiple-column_Layout">Multiple-column layout</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design">Responsive design</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Media_queries">Beginner's guide to media queries</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Legacy_Layout_Methods">Legacy layout methods</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Supporting_Older_Browsers">Supporting older browsers</a></li><li><a href="/en-US/docs/Learn/CSS/CSS_layout/Fundamental_Layout_Comprehension">Fundamental layout comprehension</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/JavaScript">JavaScript — Dynamic client-side scripting</a></li><li><details><summary>JavaScript first steps</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/First_steps">JavaScript first steps</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/What_is_JavaScript">What is JavaScript?</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/A_first_splash">A first splash into JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/What_went_wrong">What went wrong? Troubleshooting JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Variables">Storing the information you need — Variables</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Math">Basic math in JavaScript — numbers and operators</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Strings">Handling text — strings in JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods">Useful string methods</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Arrays">Arrays</a></li><li><a href="/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator">Silly story generator</a></li></ol></details></li><li><details><summary>JavaScript building blocks</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks">JavaScript building blocks</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/conditionals">Making decisions in your code — conditionals</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Looping_code">Looping code</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Functions">Functions — reusable blocks of code</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Build_your_own_function">Build your own function</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Return_values">Function return values</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Events">Introduction to events</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Event_bubbling">Event bubbling</a></li><li><a href="/en-US/docs/Learn/JavaScript/Building_blocks/Image_gallery">Image gallery</a></li></ol></details></li><li><details open=""><summary>Introducing JavaScript objects</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Objects">Introducing JavaScript objects</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Basics">JavaScript object basics</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object_prototypes">Object prototypes</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object-oriented_programming">Object-oriented programming</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Classes_in_JavaScript">Classes in JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/JSON">Working with JSON</a></li><li><a href="/en-US/docs/Learn/JavaScript/Objects/Object_building_practice">Object building practice</a></li><li><em><a href="/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features" aria-current="page">Adding features to our bouncing balls demo</a></em></li></ol></details></li><li><details><summary>Asynchronous JavaScript</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous">Asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Introducing">Introducing asynchronous JavaScript</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Promises">How to use promises</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Implementing_a_promise-based_API">How to implement a promise-based API</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Introducing_workers">Introducing workers</a></li><li><a href="/en-US/docs/Learn/JavaScript/Asynchronous/Sequencing_animations">Sequencing animations</a></li></ol></details></li><li><details><summary>Client-side web APIs</summary><ol><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs">Client-side web APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introduction">Introduction to web APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents">Manipulating documents</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Fetching_data">Fetching data from the server</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Third_party_APIs">Third-party APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Drawing_graphics">Drawing graphics</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs">Video and Audio APIs</a></li><li><a href="/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Client-side_storage">Client-side storage</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Forms">Web forms — Working with user data</a></li><li><details><summary>Web form building blocks</summary><ol><li><a href="/en-US/docs/Learn/Forms">Web form building blocks</a></li><li><a href="/en-US/docs/Learn/Forms/Your_first_form">Your first form</a></li><li><a href="/en-US/docs/Learn/Forms/How_to_structure_a_web_form">How to structure a web form</a></li><li><a href="/en-US/docs/Learn/Forms/Basic_native_form_controls">Basic native form controls</a></li><li><a href="/en-US/docs/Learn/Forms/HTML5_input_types">The HTML5 input types</a></li><li><a href="/en-US/docs/Learn/Forms/Other_form_controls">Other form controls</a></li><li><a href="/en-US/docs/Learn/Forms/Styling_web_forms">Styling web forms</a></li><li><a href="/en-US/docs/Learn/Forms/Advanced_form_styling">Advanced form styling</a></li><li><a href="/en-US/docs/Learn/Forms/UI_pseudo-classes">UI pseudo-classes</a></li><li><a href="/en-US/docs/Learn/Forms/Form_validation">Client-side form validation</a></li><li><a href="/en-US/docs/Learn/Forms/Sending_and_retrieving_form_data">Sending form data</a></li></ol></details></li><li><details><summary>Advanced web form techniques</summary><ol><li><a href="/en-US/docs/Learn/Forms/How_to_build_custom_form_controls">How to build custom form controls</a></li><li><a href="/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript">Sending forms through JavaScript</a></li><li><a href="/en-US/docs/Learn/Forms/Property_compatibility_table_for_form_controls">CSS property compatibility table for form controls</a></li><li><a href="/en-US/docs/Learn/Forms/HTML_forms_in_legacy_browsers">HTML forms in legacy browsers</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Accessibility">Accessibility — Make the web usable by everyone</a></li><li><details><summary>Accessibility guides</summary><ol><li><a href="/en-US/docs/Learn/Accessibility">Accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/What_is_accessibility">What is accessibility?</a></li><li><a href="/en-US/docs/Learn/Accessibility/HTML">HTML: A good basis for accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/CSS_and_JavaScript">CSS and JavaScript accessibility best practices</a></li><li><a href="/en-US/docs/Learn/Accessibility/WAI-ARIA_basics">WAI-ARIA basics</a></li><li><a href="/en-US/docs/Learn/Accessibility/Multimedia">Accessible multimedia</a></li><li><a href="/en-US/docs/Learn/Accessibility/Mobile">Mobile accessibility</a></li><li><a href="/en-US/docs/Learn/Accessibility/Accessibility_troubleshooting">Assessment: Accessibility troubleshooting</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Performance">Performance — Making websites fast and responsive</a></li><li><details><summary>Performance guides</summary><ol><li><a href="/en-US/docs/Learn/Performance">Web performance</a></li><li><a href="/en-US/docs/Learn/Performance/why_web_performance">The "why" of web performance</a></li><li><a href="/en-US/docs/Learn/Performance/What_is_web_performance">What is web performance?</a></li><li><a href="/en-US/docs/Learn/Performance/Perceived_performance">Perceived performance</a></li><li><a href="/en-US/docs/Learn/Performance/Measuring_performance">Measuring performance</a></li><li><a href="/en-US/docs/Learn/Performance/Multimedia">Multimedia: Images</a></li><li><a href="/en-US/docs/Learn/Performance/video">Multimedia: video</a></li><li><a href="/en-US/docs/Learn/Performance/JavaScript">JavaScript performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/HTML">HTML performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/CSS">CSS performance optimization</a></li><li><a href="/en-US/docs/Learn/Performance/business_case_for_performance">The business case for web performance</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/MathML">MathML — Writing mathematics with MathML</a></li><li><details><summary>MathML first steps</summary><ol><li><a href="/en-US/docs/Learn/MathML/First_steps">MathML first steps</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Getting_started">Getting started with MathML</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Text_containers">MathML Text Containers</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Fractions_and_roots">MathML fractions and roots</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Scripts">MathML scripted elements</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Tables">MathML tables</a></li><li><a href="/en-US/docs/Learn/MathML/First_steps/Three_famous_mathematical_formulas">Three famous mathematical formulas</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/../Games">Games — Developing games for the web</a></li><li><details><summary>Guides and tutorials</summary><ol><li><a href="/en-US/docs/Games/Introduction">Introduction to game development for the Web</a></li><li><a href="/en-US/docs/Games/Techniques">Techniques for game development</a></li><li><a href="/en-US/docs/Games/Tutorials">Tutorials</a></li><li><a href="/en-US/docs/Games/Publishing_games">Publishing games</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Tools_and_testing">Tools and testing</a></li><li><details><summary>Client-side web development tools</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools">Understanding client-side web development tools</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Overview">Client-side tooling overview</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Command_line">Command line crash course</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Package_management">Package management basics</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Introducing_complete_toolchain">Introducing a complete toolchain</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Deployment">Deploying our app</a></li></ol></details></li><li><details><summary>Introduction to client-side frameworks</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Introduction">Introduction to client-side frameworks</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Main_features">Framework main features</a></li></ol></details></li><li><details><summary>React</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_getting_started">Getting started with React</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_todo_list_beginning">Beginning our React todo list</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_components">Componentizing our React app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_events_state">React interactivity: Events and state</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_filtering_conditional_rendering">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_accessibility">Accessibility in React</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_resources">React resources</a></li></ol></details></li><li><details><summary>Ember</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_getting_started">Getting started with Ember</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_structure_componentization">Ember app structure and componentization</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_interactivity_events_state">Ember interactivity: Events, classes and state</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_conditional_footer">Ember Interactivity: Footer functionality, conditional rendering</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_routing">Routing in Ember</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_resources">Ember resources and troubleshooting</a></li></ol></details></li><li><details><summary>Vue</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_getting_started">Getting started with Vue</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_first_component">Creating our first Vue component</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_rendering_lists">Rendering a list of Vue components</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_methods_events_models">Adding a new todo form: Vue events, methods, and models</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_styling">Styling Vue components with CSS</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_computed_properties">Using Vue computed properties</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_conditional_rendering">Vue conditional rendering: editing existing todos</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_refs_focus_management">Vue refs and lifecycle methods for focus management</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_resources">Vue resources</a></li></ol></details></li><li><details><summary>Svelte</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_getting_started">Getting started with Svelte</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_Todo_list_beginning">Starting our Svelte to-do list app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_variables_props">Dynamic behavior in Svelte: working with variables and props</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_components">Componentizing our Svelte app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_reactivity_lifecycle_accessibility">Advanced Svelte: Reactivity, lifecycle, accessibility</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_stores">Working with Svelte stores</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_TypeScript">TypeScript support in Svelte</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_deployment_next">Deployment and next steps</a></li></ol></details></li><li><details><summary>Angular</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_getting_started">Getting started with Angular</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_todo_list_beginning">Beginning our Angular todo list app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_styling">Styling our Angular app</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_item_component">Creating an item component</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_filtering">Filtering our to-do items</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_building">Building Angular applications and further resources</a></li></ol></details></li><li><details><summary>Git and GitHub</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/GitHub">Git and GitHub</a></li></ol></details></li><li><details><summary>Cross browser testing</summary><ol><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing">Cross browser testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Introduction">Introduction to cross-browser testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Testing_strategies">Strategies for carrying out testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/HTML_and_CSS">Handling common HTML and CSS problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/JavaScript">Handling common JavaScript problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility">Handling common accessibility problems</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Feature_detection">Implementing feature detection</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Automated_testing">Introduction to automated testing</a></li><li><a href="/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Your_own_automation_environment">Setting up your own test automation environment</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Server-side">Server-side website programming</a></li><li><details><summary>First steps</summary><ol><li><a href="/en-US/docs/Learn/Server-side/First_steps">Server-side website programming first steps</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Introduction">Introduction to the server side</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Client-Server_overview">Client-Server Overview</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Web_frameworks">Server-side web frameworks</a></li><li><a href="/en-US/docs/Learn/Server-side/First_steps/Website_security">Website security</a></li></ol></details></li><li><details><summary>Django web framework (Python)</summary><ol><li><a href="/en-US/docs/Learn/Server-side/Django">Django Web Framework (Python)</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Introduction">Django introduction</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/development_environment">Setting up a Django development environment</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Tutorial_local_library_website">Django Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/skeleton_website">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Models">Django Tutorial Part 3: Using models</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Admin_site">Django Tutorial Part 4: Django admin site</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Home_page">Django Tutorial Part 5: Creating our home page</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Generic_views">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Sessions">Django Tutorial Part 7: Sessions framework</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Authentication">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Forms">Django Tutorial Part 9: Working with forms</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Testing">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/Deployment">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/web_application_security">Django web application security</a></li><li><a href="/en-US/docs/Learn/Server-side/Django/django_assessment_blog">Assessment: DIY Django mini blog</a></li></ol></details></li><li><details><summary>Express Web Framework (Node.js/JavaScript)</summary><ol><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs">Express web framework (Node.js/JavaScript)</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Introduction">Express/Node introduction</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/development_environment">Setting up a Node development environment</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Tutorial_local_library_website">Express Tutorial: The Local Library website</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/skeleton_website">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/mongoose">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/routes">Express Tutorial Part 4: Routes and controllers</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/Displaying_data">Express Tutorial Part 5: Displaying library data</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/forms">Express Tutorial Part 6: Working with forms</a></li><li><a href="/en-US/docs/Learn/Server-side/Express_Nodejs/deployment">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li><li class="section"><a href="/en-US/docs/Learn/Common_questions">Further resources</a></li><li><details><summary>Common questions</summary><ol><li><a href="/en-US/docs/Learn/Common_questions">Common questions</a></li><li><a href="/en-US/docs/Learn/HTML/Howto">Use HTML to solve common problems</a></li><li><a href="/en-US/docs/Learn/CSS/Howto">Use CSS to solve common problems</a></li><li><a href="/en-US/docs/Learn/JavaScript/Howto">Solve common problems in your JavaScript code</a></li><li><a href="/en-US/docs/Learn/Common_questions/Web_mechanics">Web mechanics</a></li><li><a href="/en-US/docs/Learn/Common_questions/Tools_and_setup">Tools and setup</a></li><li><a href="/en-US/docs/Learn/Common_questions/Design_and_accessibility">Design and accessibility</a></li></ol></details></li></ol></div></div><section class="place side"></section></nav></aside><div class="toc-container"><aside class="toc"><nav><div class="document-toc-container"><section class="document-toc"><header><h2 class="document-toc-heading">In this article</h2></header><ul class="document-toc-list"><li class="document-toc-item "><a class="document-toc-link" href="#starting_point">Starting point</a></li><li class="document-toc-item "><a class="document-toc-link" href="#hints_and_tips">Hints and tips</a></li><li class="document-toc-item "><a class="document-toc-link" href="#project_brief">Project brief</a></li><li class="document-toc-item "><a class="document-toc-link" href="#steps_to_complete">Steps to complete</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>Adding features to our bouncing balls demo</h1></header><div class="section-content"><ul class="prev-next"> <li><a class="button secondary" href="/en-US/docs/Learn/JavaScript/Objects/Object_building_practice"><span class="button-wrap"> Previous </span></a></li> <li><a class="button secondary" href="/en-US/docs/Learn/JavaScript/Objects"><span class="button-wrap"> Overview: Introducing JavaScript objects</span></a></li> </ul> <p>In this assessment, you are expected to use the bouncing balls demo from the previous article as a starting point, and add some new and interesting features to it.</p> <figure class="table-container"><table> <tbody> <tr> <th scope="row">Prerequisites:</th> <td> Before attempting this assessment you should have already worked through all the articles in this module. </td> </tr> <tr> <th scope="row">Objective:</th> <td> To test comprehension of JavaScript objects and object-oriented constructs </td> </tr> </tbody> </table></figure></div><section aria-labelledby="starting_point"><h2 id="starting_point"><a href="#starting_point">Starting point</a></h2><div class="section-content"><p>To get this assessment started, make a local copy of <a href="https://github.com/mdn/learning-area/blob/main/javascript/oojs/bouncing-balls/index-finished.html" class="external" target="_blank">index-finished.html</a>, <a href="https://github.com/mdn/learning-area/blob/main/javascript/oojs/bouncing-balls/style.css" class="external" target="_blank">style.css</a>, and <a href="https://github.com/mdn/learning-area/blob/main/javascript/oojs/bouncing-balls/main-finished.js" class="external" target="_blank">main-finished.js</a> from our last article in a new directory in your local computer.</p> <p>Alternatively, you could use an online editor such as <a href="https://codepen.io/" class="external" target="_blank">CodePen</a>, <a href="https://jsfiddle.net/" class="external" target="_blank">JSFiddle</a>, or <a href="https://glitch.com/" class="external" target="_blank">Glitch</a>. You could paste the HTML, CSS and JavaScript into one of these online editors. If the online editor you are using doesn't have a separate JavaScript panel, feel free to put it inline in a <code><script></code> element inside the HTML page.</p> <div class="notecard note"> <p><strong>Note:</strong> If you get stuck, you can reach out to us in one of our <a href="/en-US/docs/MDN/Community/Communication_channels">communication channels</a>.</p> </div></div></section><section aria-labelledby="hints_and_tips"><h2 id="hints_and_tips"><a href="#hints_and_tips">Hints and tips</a></h2><div class="section-content"><p>A couple of pointers before you get started.</p> <ul> <li>This assessment is quite challenging. Read the whole assessment before you start coding, and take each step slowly and carefully.</li> <li>It might be a good idea to save a separate copy of the demo after you get each stage working, so you can refer back to it if you find yourself in trouble later on.</li> </ul></div></section><section aria-labelledby="project_brief"><h2 id="project_brief"><a href="#project_brief">Project brief</a></h2><div class="section-content"><p>Our bouncy ball demo is fun, but now we want to make it a little bit more interactive by adding a user-controlled evil circle, which will eat the balls if it catches them. We also want to test your object-building skills by creating a generic <code>Shape()</code> object that our balls and evil circle can inherit from. Finally, we want to add a score counter to track the number of balls left to capture.</p> <p>The following screenshot gives you an idea of what the finished program should look like:</p> <p> <img src="/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features/bouncing-evil-circle.png" alt="Screenshot of the bouncing balls demo page. A white-outlined circle is visible in addition to the colored balls, and the text "Ball count: 23" is visible under the heading." width="800" height="533" loading="lazy"> </p> <p>To give you more of an idea, have a look at the <a href="https://mdn.github.io/learning-area/javascript/oojs/assessment/" class="external" target="_blank">finished example</a> (no peeking at the source code!)</p></div></section><section aria-labelledby="steps_to_complete"><h2 id="steps_to_complete"><a href="#steps_to_complete">Steps to complete</a></h2><div class="section-content"><p>The following sections describe what you need to do.</p></div></section><section aria-labelledby="create_a_shape_class"><h3 id="create_a_shape_class"><a href="#create_a_shape_class">Create a Shape class</a></h3><div class="section-content"><p>First of all, create a new <code>Shape</code> class. This has only a constructor. The <code>Shape</code> constructor should define the <code>x</code>, <code>y</code>, <code>velX</code>, and <code>velY</code> properties in the same way as the <code>Ball()</code> constructor did originally, but not the <code>color</code> and <code>size</code> properties.</p> <p>The <code>Ball</code> class should be made to derive from <code>Shape</code> using <code>extends</code>. The constructor for <code>Ball</code> should:</p> <ul> <li>take the same arguments as before: <code>x</code>, <code>y</code>, <code>velX</code>, <code>velY</code>, <code>size</code>, and <code>color</code></li> <li>call the <code>Shape</code> constructor using <code>super()</code>, passing in the <code>x</code>, <code>y</code>, <code>velX</code>, and <code>velY</code> arguments</li> <li>initialize its own <code>color</code> and <code>size</code> properties from the parameters it is given.</li> </ul> <p>The <code>Ball</code> constructor should define a new property called <code>exists</code>, which is used to track whether the balls exist in the program (have not been eaten by the evil circle). This should be a boolean (<code>true</code>/<code>false</code>), initialized to <code>true</code> in the constructor.</p> <p>The <code>collisionDetect()</code> method of the <code>Ball</code> class needs a small update. A ball needs to be considered for collision detection only if the <code>exists</code> property is <code>true</code>. So, replace the existing <code>collisionDetect()</code> code with the following code:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>collisionDetect() { for (const ball of balls) { if (!(this === ball) && ball.exists) { const dx = this.x - ball.x; const dy = this.y - ball.y; const distance = Math.sqrt(dx * dx + dy * dy); if (distance < this.size + ball.size) { ball.color = this.color = randomRGB(); } } } } </code></pre></div> <p>As discussed above, the only addition is to check if the ball exists — by using <code>ball.exists</code> in the <code>if</code> conditional.</p> <p>The ball <code>draw()</code> and <code>update()</code> method definitions should be able to stay exactly the same as they were before.</p> <p>At this point, try reloading the code — it should work just the same as it did before, with our redesigned objects.</p></div></section><section aria-labelledby="defining_evilcircle"><h3 id="defining_evilcircle"><a href="#defining_evilcircle">Defining EvilCircle</a></h3><div class="section-content"><p>Now it's time to meet the bad guy — the <code>EvilCircle()</code>! Our game is only going to involve one evil circle, but we are still going to define it using a constructor that inherits from <code>Shape()</code>, to give you some practice. You might want to add another circle to the app later on that can be controlled by another player, or have several computer-controlled evil circles. You're probably not going to take over the world with a single evil circle, but it will do for this assessment.</p> <p>Create a definition for an <code>EvilCircle</code> class. It should inherit from <code>Shape</code> using <code>extends</code>.</p> <h4 id="evilcircle_constructor">EvilCircle constructor</h4> <p>The constructor for <code>EvilCircle</code> should:</p> <ul> <li>be passed just <code>x</code>, <code>y</code> arguments</li> <li>pass the <code>x</code>, <code>y</code> arguments up to the <code>Shape</code> superclass along with values for <code>velX</code> and <code>velY</code> hardcoded to 20. You should do this with code like <code>super(x, y, 20, 20);</code></li> <li>set <code>color</code> to <code>white</code> and <code>size</code> to <code>10</code>.</li> </ul> <p>Finally, the constructor should set up the code enabling the user to move the evil circle around the screen:</p> <div class="code-example"><div class="example-header"><span class="language-name">js</span></div><pre class="brush: js notranslate"><code>window.addEventListener("keydown", (e) => { switch (e.key) { case "a": this.x -= this.velX; break; case "d": this.x += this.velX; break; case "w": this.y -= this.velY; break; case "s": this.y += this.velY; break; } }); </code></pre></div> <p>This adds a <code>keydown</code> event listener to the <code>window</code> object so that when a key is pressed, the event object's <a href="/en-US/docs/Web/API/KeyboardEvent/key"><code>key</code></a> property is consulted to see which key is pressed. If it is one of the four specified keys, then the evil circle will move left/right/up/down.</p></div></section><section aria-labelledby="defining_methods_for_evilcircle"><h3 id="defining_methods_for_evilcircle"><a href="#defining_methods_for_evilcircle">Defining methods for EvilCircle</a></h3><div class="section-content"><p>The <code>EvilCircle</code> class should have three methods, as described below.</p> <h4 id="draw">draw()</h4> <p>This method has the same purpose as the <code>draw()</code> method for <code>Ball</code>: it draws the object instance on the canvas. The <code>draw()</code> method for <code>EvilCircle</code> will work in a very similar way, so you can start by copying the <code>draw()</code> method for <code>Ball</code>. You should then make the following changes:</p> <ul> <li>We want the evil circle to not be filled in, but rather just have an outer line (stroke). You can achieve this by updating <a href="/en-US/docs/Web/API/CanvasRenderingContext2D/fillStyle"><code>fillStyle</code></a> and <a href="/en-US/docs/Web/API/CanvasRenderingContext2D/fill"><code>fill()</code></a> to <a href="/en-US/docs/Web/API/CanvasRenderingContext2D/strokeStyle"><code>strokeStyle</code></a> and <a href="/en-US/docs/Web/API/CanvasRenderingContext2D/stroke"><code>stroke()</code></a> respectively.</li> <li>We also want to make the stroke a bit thicker, so you can see the evil circle a bit more easily. This can be achieved by setting a value for <a href="/en-US/docs/Web/API/CanvasRenderingContext2D/lineWidth"><code>lineWidth</code></a> somewhere after the <a href="/en-US/docs/Web/API/CanvasRenderingContext2D/beginPath"><code>beginPath()</code></a> call (3 will do).</li> </ul> <h4 id="checkbounds">checkBounds()</h4> <p>This method will do the same thing as the first part of the <code>update()</code> method for <code>Ball</code> — look to see whether the evil circle is going to go off the edge of the screen, and stop it from doing so. Again, you can mostly just copy the <code>update()</code> method for <code>Ball</code>, but there are a few changes you should make:</p> <ul> <li>Get rid of the last two lines — we don't want to automatically update the evil circle's position on every frame, because we will be moving it in some other way, as you'll see below.</li> <li>Inside the <code>if ()</code> statements, if the tests return true we don't want to update <code>velX</code>/<code>velY</code>; we want to instead change the value of <code>x</code>/<code>y</code> so the evil circle is bounced back onto the screen slightly. Adding or subtracting (as appropriate) the evil circle's <code>size</code> property would make sense.</li> </ul> <h4 id="collisiondetect">collisionDetect()</h4> <p>This method will act in a very similar way to the <code>collisionDetect()</code> method for <code>Ball</code> method, so you can use a copy of that as the basis of this new method. But there are a couple of differences:</p> <ul> <li>In the outer <code>if</code> statement, you no longer need to check whether the current ball in the iteration is the same as the ball that is doing the checking — because it is no longer a ball, it is the evil circle! Instead, you need to do a test to see if the ball being checked exists (with which property could you do this with?). If it doesn't exist, it has already been eaten by the evil circle, so there is no need to check it again.</li> <li>In the inner <code>if</code> statement, you no longer want to make the objects change color when a collision is detected — instead, you want to set any balls that collide with the evil circle to not exist any more (again, how do you think you'd do that?).</li> </ul></div></section><section aria-labelledby="bringing_the_evil_circle_into_the_program"><h3 id="bringing_the_evil_circle_into_the_program"><a href="#bringing_the_evil_circle_into_the_program">Bringing the evil circle into the program</a></h3><div class="section-content"><p>Now we've defined the evil circle, we need to actually make it appear in our scene. To do this, you need to make some changes to the <code>loop()</code> function.</p> <ul> <li>First of all, create a new evil circle object instance (specifying the necessary parameters). You only need to do this once, not on every iteration of the loop.</li> <li>At the point where you loop through every ball and call the <code>draw()</code>, <code>update()</code>, and <code>collisionDetect()</code> functions for each one, make it so that these functions are only called if the current ball exists.</li> <li>Call the evil circle instance's <code>draw()</code>, <code>checkBounds()</code>, and <code>collisionDetect()</code> methods on every iteration of the loop.</li> </ul></div></section><section aria-labelledby="implementing_the_score_counter"><h3 id="implementing_the_score_counter"><a href="#implementing_the_score_counter">Implementing the score counter</a></h3><div class="section-content"><p>To implement the score counter, follow the following steps:</p> <ol> <li> <p>In your HTML file, add a <a href="/en-US/docs/Web/HTML/Element/p"><code><p></code></a> element just below the <a href="/en-US/docs/Web/HTML/Element/Heading_Elements">h1</a> element containing the text "Ball count: ".</p> </li> <li> <p>In your CSS file, add the following rule at the bottom:</p> <div class="code-example"><div class="example-header"><span class="language-name">css</span></div><pre class="brush: css notranslate"><code>p { position: absolute; margin: 0; top: 35px; right: 5px; color: #aaa; } </code></pre></div> </li> <li> <p>In your JavaScript, make the following updates:</p> <ul> <li>Create a variable that stores a reference to the paragraph.</li> <li>Keep a count of the number of balls on screen in some way.</li> <li>Increment the count and display the updated number of balls each time a ball is added to the scene.</li> <li>Decrement the count and display the updated number of balls each time the evil circle eats a ball (causes it not to exist).</li> </ul> </li> </ol><ul class="prev-next"> <li><a class="button secondary" href="/en-US/docs/Learn/JavaScript/Objects/Object_building_practice"><span class="button-wrap"> Previous </span></a></li> <li><a class="button secondary" 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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/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features","doc":{"isMarkdown":true,"isTranslated":false,"isActive":true,"flaws":{},"title":"Adding features to our bouncing balls demo","mdn_url":"/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features","locale":"en-US","native":"English (US)","sidebarHTML":"<ol><li class=\"section\"><a href=\"/en-US/docs/Learn/Getting_started_with_the_web\">Complete beginners start here!</a></li><li><details><summary>Getting started with the web</summary><ol><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web\">Getting started with the web</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Installing_basic_software\">Installing basic software</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/What_will_your_website_look_like\">What will your website look like?</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Dealing_with_files\">Dealing with files</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/HTML_basics\">HTML basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/CSS_basics\">CSS basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics\">JavaScript basics</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/Publishing_your_website\">Publishing your website</a></li><li><a href=\"/en-US/docs/Learn/Getting_started_with_the_web/How_the_Web_works\">How the web works</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/HTML\">HTML — Structuring the web</a></li><li><details><summary>Introduction to HTML</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML\">Introduction to HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Getting_started\">Getting started with HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/The_head_metadata_in_HTML\">What's in the head? Metadata in HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals\">HTML text fundamentals</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Creating_hyperlinks\">Creating hyperlinks</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Advanced_text_formatting\">Advanced text formatting</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Document_and_website_structure\">Document and website structure</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Debugging_HTML\">Debugging HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Marking_up_a_letter\">Marking up a letter</a></li><li><a href=\"/en-US/docs/Learn/HTML/Introduction_to_HTML/Structuring_a_page_of_content\">Structuring a page of content</a></li></ol></details></li><li><details><summary>Multimedia and embedding</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding\">Multimedia and embedding</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Images_in_HTML\">Images in HTML</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Video_and_audio_content\">Video and audio content</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Other_embedding_technologies\">From object to iframe — other embedding technologies</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Adding_vector_graphics_to_the_Web\">Adding vector graphics to the web</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Responsive_images\">Responsive images</a></li><li><a href=\"/en-US/docs/Learn/HTML/Multimedia_and_embedding/Mozilla_splash_page\">Mozilla splash page</a></li></ol></details></li><li><details><summary>HTML tables</summary><ol><li><a href=\"/en-US/docs/Learn/HTML/Tables\">HTML tables</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Basics\">HTML table basics</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Advanced\">HTML table advanced features and accessibility</a></li><li><a href=\"/en-US/docs/Learn/HTML/Tables/Structuring_planet_data\">Structuring planet data</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/CSS\">CSS — Styling the web</a></li><li><details><summary>CSS first steps</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/First_steps\">CSS first steps</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/What_is_CSS\">What is CSS?</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/Getting_started\">Getting started with CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/How_CSS_is_structured\">How CSS is structured</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/How_CSS_works\">How CSS works</a></li><li><a href=\"/en-US/docs/Learn/CSS/First_steps/Styling_a_biography_page\">Styling a biography page</a></li></ol></details></li><li><details><summary>CSS building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks\">CSS building blocks</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors\">CSS selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Type_Class_and_ID_Selectors\">Type, class, and ID selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Attribute_selectors\">Attribute selectors</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Pseudo-classes_and_pseudo-elements\">Pseudo-classes and pseudo-elements</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators\">Combinators</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Cascade_and_inheritance\">Cascade, specificity, and inheritance</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Cascade_layers\">Cascade layers</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/The_box_model\">The box model</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Backgrounds_and_borders\">Backgrounds and borders</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Handling_different_text_directions\">Handling different text directions</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Overflowing_content\">Overflowing content</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Values_and_units\">CSS values and units</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Sizing_items_in_CSS\">Sizing items in CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Images_media_form_elements\">Images, media, and form elements</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Styling_tables\">Styling tables</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Advanced_styling_effects\">Advanced styling effects</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Debugging_CSS\">Debugging CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Organizing\">Organizing your CSS</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Fundamental_CSS_comprehension\">Fundamental CSS comprehension</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/Creating_fancy_letterheaded_paper\">Creating fancy letterheaded paper</a></li><li><a href=\"/en-US/docs/Learn/CSS/Building_blocks/A_cool_looking_box\">A cool-looking box</a></li></ol></details></li><li><details><summary>Styling text</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/Styling_text\">CSS styling text</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Fundamentals\">Fundamental text and font styling</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Styling_lists\">Styling lists</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Styling_links\">Styling links</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Web_fonts\">Web fonts</a></li><li><a href=\"/en-US/docs/Learn/CSS/Styling_text/Typesetting_a_homepage\">Typesetting a community school homepage</a></li></ol></details></li><li><details><summary>CSS layout</summary><ol><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout\">CSS layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Introduction\">Introduction to CSS layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Normal_Flow\">Normal Flow</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Flexbox\">Flexbox</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Grids\">Grids</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Floats\">Floats</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Positioning\">Positioning</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Multiple-column_Layout\">Multiple-column layout</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Responsive_Design\">Responsive design</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Media_queries\">Beginner's guide to media queries</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Legacy_Layout_Methods\">Legacy layout methods</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Supporting_Older_Browsers\">Supporting older browsers</a></li><li><a href=\"/en-US/docs/Learn/CSS/CSS_layout/Fundamental_Layout_Comprehension\">Fundamental layout comprehension</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/JavaScript\">JavaScript — Dynamic client-side scripting</a></li><li><details><summary>JavaScript first steps</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps\">JavaScript first steps</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/What_is_JavaScript\">What is JavaScript?</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/A_first_splash\">A first splash into JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/What_went_wrong\">What went wrong? Troubleshooting JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Variables\">Storing the information you need — Variables</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Math\">Basic math in JavaScript — numbers and operators</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Strings\">Handling text — strings in JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Useful_string_methods\">Useful string methods</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Arrays\">Arrays</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/First_steps/Silly_story_generator\">Silly story generator</a></li></ol></details></li><li><details><summary>JavaScript building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks\">JavaScript building blocks</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/conditionals\">Making decisions in your code — conditionals</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Looping_code\">Looping code</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Functions\">Functions — reusable blocks of code</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Build_your_own_function\">Build your own function</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Return_values\">Function return values</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Events\">Introduction to events</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Event_bubbling\">Event bubbling</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Building_blocks/Image_gallery\">Image gallery</a></li></ol></details></li><li><details open=\"\"><summary>Introducing JavaScript objects</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Objects\">Introducing JavaScript objects</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Basics\">JavaScript object basics</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object_prototypes\">Object prototypes</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object-oriented_programming\">Object-oriented programming</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Classes_in_JavaScript\">Classes in JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/JSON\">Working with JSON</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Objects/Object_building_practice\">Object building practice</a></li><li><em><a href=\"/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features\" aria-current=\"page\">Adding features to our bouncing balls demo</a></em></li></ol></details></li><li><details><summary>Asynchronous JavaScript</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous\">Asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Introducing\">Introducing asynchronous JavaScript</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Promises\">How to use promises</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Implementing_a_promise-based_API\">How to implement a promise-based API</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Introducing_workers\">Introducing workers</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Asynchronous/Sequencing_animations\">Sequencing animations</a></li></ol></details></li><li><details><summary>Client-side web APIs</summary><ol><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs\">Client-side web APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Introduction\">Introduction to web APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Manipulating_documents\">Manipulating documents</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Fetching_data\">Fetching data from the server</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Third_party_APIs\">Third-party APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Drawing_graphics\">Drawing graphics</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Video_and_audio_APIs\">Video and Audio APIs</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Client-side_web_APIs/Client-side_storage\">Client-side storage</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Forms\">Web forms — Working with user data</a></li><li><details><summary>Web form building blocks</summary><ol><li><a href=\"/en-US/docs/Learn/Forms\">Web form building blocks</a></li><li><a href=\"/en-US/docs/Learn/Forms/Your_first_form\">Your first form</a></li><li><a href=\"/en-US/docs/Learn/Forms/How_to_structure_a_web_form\">How to structure a web form</a></li><li><a href=\"/en-US/docs/Learn/Forms/Basic_native_form_controls\">Basic native form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/HTML5_input_types\">The HTML5 input types</a></li><li><a href=\"/en-US/docs/Learn/Forms/Other_form_controls\">Other form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/Styling_web_forms\">Styling web forms</a></li><li><a href=\"/en-US/docs/Learn/Forms/Advanced_form_styling\">Advanced form styling</a></li><li><a href=\"/en-US/docs/Learn/Forms/UI_pseudo-classes\">UI pseudo-classes</a></li><li><a href=\"/en-US/docs/Learn/Forms/Form_validation\">Client-side form validation</a></li><li><a href=\"/en-US/docs/Learn/Forms/Sending_and_retrieving_form_data\">Sending form data</a></li></ol></details></li><li><details><summary>Advanced web form techniques</summary><ol><li><a href=\"/en-US/docs/Learn/Forms/How_to_build_custom_form_controls\">How to build custom form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/Sending_forms_through_JavaScript\">Sending forms through JavaScript</a></li><li><a href=\"/en-US/docs/Learn/Forms/Property_compatibility_table_for_form_controls\">CSS property compatibility table for form controls</a></li><li><a href=\"/en-US/docs/Learn/Forms/HTML_forms_in_legacy_browsers\">HTML forms in legacy browsers</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Accessibility\">Accessibility — Make the web usable by everyone</a></li><li><details><summary>Accessibility guides</summary><ol><li><a href=\"/en-US/docs/Learn/Accessibility\">Accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/What_is_accessibility\">What is accessibility?</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/HTML\">HTML: A good basis for accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/CSS_and_JavaScript\">CSS and JavaScript accessibility best practices</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/WAI-ARIA_basics\">WAI-ARIA basics</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Multimedia\">Accessible multimedia</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Mobile\">Mobile accessibility</a></li><li><a href=\"/en-US/docs/Learn/Accessibility/Accessibility_troubleshooting\">Assessment: Accessibility troubleshooting</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Performance\">Performance — Making websites fast and responsive</a></li><li><details><summary>Performance guides</summary><ol><li><a href=\"/en-US/docs/Learn/Performance\">Web performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/why_web_performance\">The \"why\" of web performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/What_is_web_performance\">What is web performance?</a></li><li><a href=\"/en-US/docs/Learn/Performance/Perceived_performance\">Perceived performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/Measuring_performance\">Measuring performance</a></li><li><a href=\"/en-US/docs/Learn/Performance/Multimedia\">Multimedia: Images</a></li><li><a href=\"/en-US/docs/Learn/Performance/video\">Multimedia: video</a></li><li><a href=\"/en-US/docs/Learn/Performance/JavaScript\">JavaScript performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/HTML\">HTML performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/CSS\">CSS performance optimization</a></li><li><a href=\"/en-US/docs/Learn/Performance/business_case_for_performance\">The business case for web performance</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/MathML\">MathML — Writing mathematics with MathML</a></li><li><details><summary>MathML first steps</summary><ol><li><a href=\"/en-US/docs/Learn/MathML/First_steps\">MathML first steps</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Getting_started\">Getting started with MathML</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Text_containers\">MathML Text Containers</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Fractions_and_roots\">MathML fractions and roots</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Scripts\">MathML scripted elements</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Tables\">MathML tables</a></li><li><a href=\"/en-US/docs/Learn/MathML/First_steps/Three_famous_mathematical_formulas\">Three famous mathematical formulas</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/../Games\">Games — Developing games for the web</a></li><li><details><summary>Guides and tutorials</summary><ol><li><a href=\"/en-US/docs/Games/Introduction\">Introduction to game development for the Web</a></li><li><a href=\"/en-US/docs/Games/Techniques\">Techniques for game development</a></li><li><a href=\"/en-US/docs/Games/Tutorials\">Tutorials</a></li><li><a href=\"/en-US/docs/Games/Publishing_games\">Publishing games</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Tools_and_testing\">Tools and testing</a></li><li><details><summary>Client-side web development tools</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools\">Understanding client-side web development tools</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Overview\">Client-side tooling overview</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Command_line\">Command line crash course</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Package_management\">Package management basics</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Introducing_complete_toolchain\">Introducing a complete toolchain</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Understanding_client-side_tools/Deployment\">Deploying our app</a></li></ol></details></li><li><details><summary>Introduction to client-side frameworks</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Introduction\">Introduction to client-side frameworks</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Main_features\">Framework main features</a></li></ol></details></li><li><details><summary>React</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_getting_started\">Getting started with React</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_todo_list_beginning\">Beginning our React todo list</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_components\">Componentizing our React app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_events_state\">React interactivity: Events and state</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_interactivity_filtering_conditional_rendering\">React interactivity: Editing, filtering, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_accessibility\">Accessibility in React</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/React_resources\">React resources</a></li></ol></details></li><li><details><summary>Ember</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_getting_started\">Getting started with Ember</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_structure_componentization\">Ember app structure and componentization</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_interactivity_events_state\">Ember interactivity: Events, classes and state</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_conditional_footer\">Ember Interactivity: Footer functionality, conditional rendering</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_routing\">Routing in Ember</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Ember_resources\">Ember resources and troubleshooting</a></li></ol></details></li><li><details><summary>Vue</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_getting_started\">Getting started with Vue</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_first_component\">Creating our first Vue component</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_rendering_lists\">Rendering a list of Vue components</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_methods_events_models\">Adding a new todo form: Vue events, methods, and models</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_styling\">Styling Vue components with CSS</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_computed_properties\">Using Vue computed properties</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_conditional_rendering\">Vue conditional rendering: editing existing todos</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_refs_focus_management\">Vue refs and lifecycle methods for focus management</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Vue_resources\">Vue resources</a></li></ol></details></li><li><details><summary>Svelte</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_getting_started\">Getting started with Svelte</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_Todo_list_beginning\">Starting our Svelte to-do list app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_variables_props\">Dynamic behavior in Svelte: working with variables and props</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_components\">Componentizing our Svelte app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_reactivity_lifecycle_accessibility\">Advanced Svelte: Reactivity, lifecycle, accessibility</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_stores\">Working with Svelte stores</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_TypeScript\">TypeScript support in Svelte</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Svelte_deployment_next\">Deployment and next steps</a></li></ol></details></li><li><details><summary>Angular</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_getting_started\">Getting started with Angular</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_todo_list_beginning\">Beginning our Angular todo list app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_styling\">Styling our Angular app</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_item_component\">Creating an item component</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_filtering\">Filtering our to-do items</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Client-side_JavaScript_frameworks/Angular_building\">Building Angular applications and further resources</a></li></ol></details></li><li><details><summary>Git and GitHub</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/GitHub\">Git and GitHub</a></li></ol></details></li><li><details><summary>Cross browser testing</summary><ol><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing\">Cross browser testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Introduction\">Introduction to cross-browser testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Testing_strategies\">Strategies for carrying out testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/HTML_and_CSS\">Handling common HTML and CSS problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/JavaScript\">Handling common JavaScript problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Accessibility\">Handling common accessibility problems</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Feature_detection\">Implementing feature detection</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Automated_testing\">Introduction to automated testing</a></li><li><a href=\"/en-US/docs/Learn/Tools_and_testing/Cross_browser_testing/Your_own_automation_environment\">Setting up your own test automation environment</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Server-side\">Server-side website programming</a></li><li><details><summary>First steps</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/First_steps\">Server-side website programming first steps</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Introduction\">Introduction to the server side</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Client-Server_overview\">Client-Server Overview</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Web_frameworks\">Server-side web frameworks</a></li><li><a href=\"/en-US/docs/Learn/Server-side/First_steps/Website_security\">Website security</a></li></ol></details></li><li><details><summary>Django web framework (Python)</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/Django\">Django Web Framework (Python)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Introduction\">Django introduction</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/development_environment\">Setting up a Django development environment</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Tutorial_local_library_website\">Django Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/skeleton_website\">Django Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Models\">Django Tutorial Part 3: Using models</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Admin_site\">Django Tutorial Part 4: Django admin site</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Home_page\">Django Tutorial Part 5: Creating our home page</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Generic_views\">Django Tutorial Part 6: Generic list and detail views</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Sessions\">Django Tutorial Part 7: Sessions framework</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Authentication\">Django Tutorial Part 8: User authentication and permissions</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Forms\">Django Tutorial Part 9: Working with forms</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Testing\">Django Tutorial Part 10: Testing a Django web application</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/Deployment\">Django Tutorial Part 11: Deploying Django to production</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/web_application_security\">Django web application security</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Django/django_assessment_blog\">Assessment: DIY Django mini blog</a></li></ol></details></li><li><details><summary>Express Web Framework (Node.js/JavaScript)</summary><ol><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs\">Express web framework (Node.js/JavaScript)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Introduction\">Express/Node introduction</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/development_environment\">Setting up a Node development environment</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Tutorial_local_library_website\">Express Tutorial: The Local Library website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/skeleton_website\">Express Tutorial Part 2: Creating a skeleton website</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/mongoose\">Express Tutorial Part 3: Using a Database (with Mongoose)</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/routes\">Express Tutorial Part 4: Routes and controllers</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/Displaying_data\">Express Tutorial Part 5: Displaying library data</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/forms\">Express Tutorial Part 6: Working with forms</a></li><li><a href=\"/en-US/docs/Learn/Server-side/Express_Nodejs/deployment\">Express Tutorial Part 7: Deploying to production</a></li></ol></details></li><li class=\"section\"><a href=\"/en-US/docs/Learn/Common_questions\">Further resources</a></li><li><details><summary>Common questions</summary><ol><li><a href=\"/en-US/docs/Learn/Common_questions\">Common questions</a></li><li><a href=\"/en-US/docs/Learn/HTML/Howto\">Use HTML to solve common problems</a></li><li><a href=\"/en-US/docs/Learn/CSS/Howto\">Use CSS to solve common problems</a></li><li><a href=\"/en-US/docs/Learn/JavaScript/Howto\">Solve common problems in your JavaScript code</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Web_mechanics\">Web mechanics</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Tools_and_setup\">Tools and setup</a></li><li><a href=\"/en-US/docs/Learn/Common_questions/Design_and_accessibility\">Design and accessibility</a></li></ol></details></li></ol>","sidebarMacro":"LearnSidebar","body":[{"type":"prose","value":{"id":null,"title":null,"isH3":false,"content":"<ul class=\"prev-next\">\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/Objects/Object_building_practice\"><span class=\"button-wrap\"> Previous </span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/Objects\"><span class=\"button-wrap\"> Overview: Introducing JavaScript objects</span></a></li>\n \n</ul>\n<p>In this assessment, you are expected to use the bouncing balls demo from the previous article as a starting point, and add some new and interesting features to it.</p>\n<figure class=\"table-container\"><table>\n <tbody>\n <tr>\n <th scope=\"row\">Prerequisites:</th>\n <td>\n Before attempting this assessment you should have already worked through\n all the articles in this module.\n </td>\n </tr>\n <tr>\n <th scope=\"row\">Objective:</th>\n <td>\n To test comprehension of JavaScript objects and object-oriented\n constructs\n </td>\n </tr>\n </tbody>\n</table></figure>"}},{"type":"prose","value":{"id":"starting_point","title":"Starting point","isH3":false,"content":"<p>To get this assessment started, make a local copy of <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/oojs/bouncing-balls/index-finished.html\" class=\"external\" target=\"_blank\">index-finished.html</a>, <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/oojs/bouncing-balls/style.css\" class=\"external\" target=\"_blank\">style.css</a>, and <a href=\"https://github.com/mdn/learning-area/blob/main/javascript/oojs/bouncing-balls/main-finished.js\" class=\"external\" target=\"_blank\">main-finished.js</a> from our last article in a new directory in your local computer.</p>\n<p>Alternatively, you could use an online editor such as <a href=\"https://codepen.io/\" class=\"external\" target=\"_blank\">CodePen</a>, <a href=\"https://jsfiddle.net/\" class=\"external\" target=\"_blank\">JSFiddle</a>, or <a href=\"https://glitch.com/\" class=\"external\" target=\"_blank\">Glitch</a>. You could paste the HTML, CSS and JavaScript into one of these online editors. If the online editor you are using doesn't have a separate JavaScript panel, feel free to put it inline in a <code><script></code> element inside the HTML page.</p>\n<div class=\"notecard note\">\n <p><strong>Note:</strong> If you get stuck, you can reach out to us in one of our <a href=\"/en-US/docs/MDN/Community/Communication_channels\">communication channels</a>.</p>\n</div>"}},{"type":"prose","value":{"id":"hints_and_tips","title":"Hints and tips","isH3":false,"content":"<p>A couple of pointers before you get started.</p>\n<ul>\n <li>This assessment is quite challenging. Read the whole assessment before you start coding, and take each step slowly and carefully.</li>\n <li>It might be a good idea to save a separate copy of the demo after you get each stage working, so you can refer back to it if you find yourself in trouble later on.</li>\n</ul>"}},{"type":"prose","value":{"id":"project_brief","title":"Project brief","isH3":false,"content":"<p>Our bouncy ball demo is fun, but now we want to make it a little bit more interactive by adding a user-controlled evil circle, which will eat the balls if it catches them. We also want to test your object-building skills by creating a generic <code>Shape()</code> object that our balls and evil circle can inherit from. Finally, we want to add a score counter to track the number of balls left to capture.</p>\n<p>The following screenshot gives you an idea of what the finished program should look like:</p>\n<p>\n <img src=\"/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features/bouncing-evil-circle.png\" alt=\"Screenshot of the bouncing balls demo page. A white-outlined circle is visible in addition to the colored balls, and the text "Ball count: 23" is visible under the heading.\" width=\"800\" height=\"533\" loading=\"lazy\">\n</p>\n<p>To give you more of an idea, have a look at the <a href=\"https://mdn.github.io/learning-area/javascript/oojs/assessment/\" class=\"external\" target=\"_blank\">finished example</a> (no peeking at the source code!)</p>"}},{"type":"prose","value":{"id":"steps_to_complete","title":"Steps to complete","isH3":false,"content":"<p>The following sections describe what you need to do.</p>"}},{"type":"prose","value":{"id":"create_a_shape_class","title":"Create a Shape class","isH3":true,"content":"<p>First of all, create a new <code>Shape</code> class. This has only a constructor. The <code>Shape</code> constructor should define the <code>x</code>, <code>y</code>, <code>velX</code>, and <code>velY</code> properties in the same way as the <code>Ball()</code> constructor did originally, but not the <code>color</code> and <code>size</code> properties.</p>\n<p>The <code>Ball</code> class should be made to derive from <code>Shape</code> using <code>extends</code>. The constructor for <code>Ball</code> should:</p>\n<ul>\n <li>take the same arguments as before: <code>x</code>, <code>y</code>, <code>velX</code>, <code>velY</code>, <code>size</code>, and <code>color</code></li>\n <li>call the <code>Shape</code> constructor using <code>super()</code>, passing in the <code>x</code>, <code>y</code>, <code>velX</code>, and <code>velY</code> arguments</li>\n <li>initialize its own <code>color</code> and <code>size</code> properties from the parameters it is given.</li>\n</ul>\n<p>The <code>Ball</code> constructor should define a new property called <code>exists</code>, which is used to track whether the balls exist in the program (have not been eaten by the evil circle). This should be a boolean (<code>true</code>/<code>false</code>), initialized to <code>true</code> in the constructor.</p>\n<p>The <code>collisionDetect()</code> method of the <code>Ball</code> class needs a small update. A ball needs to be considered for collision detection only if the <code>exists</code> property is <code>true</code>. So, replace the existing <code>collisionDetect()</code> code with the following code:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>collisionDetect() {\n for (const ball of balls) {\n if (!(this === ball) && ball.exists) {\n const dx = this.x - ball.x;\n const dy = this.y - ball.y;\n const distance = Math.sqrt(dx * dx + dy * dy);\n\n if (distance < this.size + ball.size) {\n ball.color = this.color = randomRGB();\n }\n }\n }\n}\n</code></pre></div>\n<p>As discussed above, the only addition is to check if the ball exists — by using <code>ball.exists</code> in the <code>if</code> conditional.</p>\n<p>The ball <code>draw()</code> and <code>update()</code> method definitions should be able to stay exactly the same as they were before.</p>\n<p>At this point, try reloading the code — it should work just the same as it did before, with our redesigned objects.</p>"}},{"type":"prose","value":{"id":"defining_evilcircle","title":"Defining EvilCircle","isH3":true,"content":"<p>Now it's time to meet the bad guy — the <code>EvilCircle()</code>! Our game is only going to involve one evil circle, but we are still going to define it using a constructor that inherits from <code>Shape()</code>, to give you some practice. You might want to add another circle to the app later on that can be controlled by another player, or have several computer-controlled evil circles. You're probably not going to take over the world with a single evil circle, but it will do for this assessment.</p>\n<p>Create a definition for an <code>EvilCircle</code> class. It should inherit from <code>Shape</code> using <code>extends</code>.</p>\n<h4 id=\"evilcircle_constructor\">EvilCircle constructor</h4>\n<p>The constructor for <code>EvilCircle</code> should:</p>\n<ul>\n <li>be passed just <code>x</code>, <code>y</code> arguments</li>\n <li>pass the <code>x</code>, <code>y</code> arguments up to the <code>Shape</code> superclass along with values for <code>velX</code> and <code>velY</code> hardcoded to 20. You should do this with code like <code>super(x, y, 20, 20);</code></li>\n <li>set <code>color</code> to <code>white</code> and <code>size</code> to <code>10</code>.</li>\n</ul>\n<p>Finally, the constructor should set up the code enabling the user to move the evil circle around the screen:</p>\n<div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">js</span></div><pre class=\"brush: js notranslate\"><code>window.addEventListener(\"keydown\", (e) => {\n switch (e.key) {\n case \"a\":\n this.x -= this.velX;\n break;\n case \"d\":\n this.x += this.velX;\n break;\n case \"w\":\n this.y -= this.velY;\n break;\n case \"s\":\n this.y += this.velY;\n break;\n }\n});\n</code></pre></div>\n<p>This adds a <code>keydown</code> event listener to the <code>window</code> object so that when a key is pressed, the event object's <a href=\"/en-US/docs/Web/API/KeyboardEvent/key\"><code>key</code></a> property is consulted to see which key is pressed. If it is one of the four specified keys, then the evil circle will move left/right/up/down.</p>"}},{"type":"prose","value":{"id":"defining_methods_for_evilcircle","title":"Defining methods for EvilCircle","isH3":true,"content":"<p>The <code>EvilCircle</code> class should have three methods, as described below.</p>\n<h4 id=\"draw\">draw()</h4>\n<p>This method has the same purpose as the <code>draw()</code> method for <code>Ball</code>: it draws the object instance on the canvas. The <code>draw()</code> method for <code>EvilCircle</code> will work in a very similar way, so you can start by copying the <code>draw()</code> method for <code>Ball</code>. You should then make the following changes:</p>\n<ul>\n <li>We want the evil circle to not be filled in, but rather just have an outer line (stroke). You can achieve this by updating <a href=\"/en-US/docs/Web/API/CanvasRenderingContext2D/fillStyle\"><code>fillStyle</code></a> and <a href=\"/en-US/docs/Web/API/CanvasRenderingContext2D/fill\"><code>fill()</code></a> to <a href=\"/en-US/docs/Web/API/CanvasRenderingContext2D/strokeStyle\"><code>strokeStyle</code></a> and <a href=\"/en-US/docs/Web/API/CanvasRenderingContext2D/stroke\"><code>stroke()</code></a> respectively.</li>\n <li>We also want to make the stroke a bit thicker, so you can see the evil circle a bit more easily. This can be achieved by setting a value for <a href=\"/en-US/docs/Web/API/CanvasRenderingContext2D/lineWidth\"><code>lineWidth</code></a> somewhere after the <a href=\"/en-US/docs/Web/API/CanvasRenderingContext2D/beginPath\"><code>beginPath()</code></a> call (3 will do).</li>\n</ul>\n<h4 id=\"checkbounds\">checkBounds()</h4>\n<p>This method will do the same thing as the first part of the <code>update()</code> method for <code>Ball</code> — look to see whether the evil circle is going to go off the edge of the screen, and stop it from doing so. Again, you can mostly just copy the <code>update()</code> method for <code>Ball</code>, but there are a few changes you should make:</p>\n<ul>\n <li>Get rid of the last two lines — we don't want to automatically update the evil circle's position on every frame, because we will be moving it in some other way, as you'll see below.</li>\n <li>Inside the <code>if ()</code> statements, if the tests return true we don't want to update <code>velX</code>/<code>velY</code>; we want to instead change the value of <code>x</code>/<code>y</code> so the evil circle is bounced back onto the screen slightly. Adding or subtracting (as appropriate) the evil circle's <code>size</code> property would make sense.</li>\n</ul>\n<h4 id=\"collisiondetect\">collisionDetect()</h4>\n<p>This method will act in a very similar way to the <code>collisionDetect()</code> method for <code>Ball</code> method, so you can use a copy of that as the basis of this new method. But there are a couple of differences:</p>\n<ul>\n <li>In the outer <code>if</code> statement, you no longer need to check whether the current ball in the iteration is the same as the ball that is doing the checking — because it is no longer a ball, it is the evil circle! Instead, you need to do a test to see if the ball being checked exists (with which property could you do this with?). If it doesn't exist, it has already been eaten by the evil circle, so there is no need to check it again.</li>\n <li>In the inner <code>if</code> statement, you no longer want to make the objects change color when a collision is detected — instead, you want to set any balls that collide with the evil circle to not exist any more (again, how do you think you'd do that?).</li>\n</ul>"}},{"type":"prose","value":{"id":"bringing_the_evil_circle_into_the_program","title":"Bringing the evil circle into the program","isH3":true,"content":"<p>Now we've defined the evil circle, we need to actually make it appear in our scene. To do this, you need to make some changes to the <code>loop()</code> function.</p>\n<ul>\n <li>First of all, create a new evil circle object instance (specifying the necessary parameters). You only need to do this once, not on every iteration of the loop.</li>\n <li>At the point where you loop through every ball and call the <code>draw()</code>, <code>update()</code>, and <code>collisionDetect()</code> functions for each one, make it so that these functions are only called if the current ball exists.</li>\n <li>Call the evil circle instance's <code>draw()</code>, <code>checkBounds()</code>, and <code>collisionDetect()</code> methods on every iteration of the loop.</li>\n</ul>"}},{"type":"prose","value":{"id":"implementing_the_score_counter","title":"Implementing the score counter","isH3":true,"content":"<p>To implement the score counter, follow the following steps:</p>\n<ol>\n <li>\n <p>In your HTML file, add a <a href=\"/en-US/docs/Web/HTML/Element/p\"><code><p></code></a> element just below the <a href=\"/en-US/docs/Web/HTML/Element/Heading_Elements\">h1</a> element containing the text \"Ball count: \".</p>\n </li>\n <li>\n <p>In your CSS file, add the following rule at the bottom:</p>\n <div class=\"code-example\"><div class=\"example-header\"><span class=\"language-name\">css</span></div><pre class=\"brush: css notranslate\"><code>p {\n position: absolute;\n margin: 0;\n top: 35px;\n right: 5px;\n color: #aaa;\n}\n</code></pre></div>\n </li>\n <li>\n <p>In your JavaScript, make the following updates:</p>\n <ul>\n <li>Create a variable that stores a reference to the paragraph.</li>\n <li>Keep a count of the number of balls on screen in some way.</li>\n <li>Increment the count and display the updated number of balls each time a ball is added to the scene.</li>\n <li>Decrement the count and display the updated number of balls each time the evil circle eats a ball (causes it not to exist).</li>\n </ul>\n </li>\n</ol><ul class=\"prev-next\">\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/Objects/Object_building_practice\"><span class=\"button-wrap\"> Previous </span></a></li>\n <li><a class=\"button secondary\" href=\"/en-US/docs/Learn/JavaScript/Objects\"><span class=\"button-wrap\"> Overview: Introducing JavaScript objects</span></a></li>\n \n</ul>"}}],"toc":[{"text":"Starting point","id":"starting_point"},{"text":"Hints and tips","id":"hints_and_tips"},{"text":"Project brief","id":"project_brief"},{"text":"Steps to complete","id":"steps_to_complete"}],"summary":"In this assessment, you are expected to use the bouncing balls demo from the previous article as a starting point, and add some new and interesting features to it.","popularity":0.0039,"modified":"2024-07-25T21:20:22.000Z","other_translations":[{"locale":"de","title":"Hinzufügen von Funktionen zu unserem hüpfenden Kugeln-Demo","native":"Deutsch"},{"locale":"es","title":"Añadiendo características a nuestra demo de bouncing balls","native":"Español"},{"locale":"fr","title":"Ajouter des fonctionnalités à notre exercice des balles rebondissantes","native":"Français"},{"locale":"ja","title":"バウンスボールのデモに機能を追加する","native":"日本語"},{"locale":"pt-BR","title":"Adicionando recursos à nossa demonstração de bolas pulantes","native":"Português (do Brasil)"},{"locale":"ru","title":"Добавление функций в нашу демонстрацию отбойных шаров","native":"Русский"},{"locale":"zh-CN","title":"为“弹球”示例添加新功能","native":"中文 (简体)"},{"locale":"zh-TW","title":"為彈跳彩球添增其他功能","native":"正體中文 (繁體)"}],"pageType":"learn-module-assessment","source":{"folder":"en-us/learn/javascript/objects/adding_bouncing_balls_features","github_url":"https://github.com/mdn/content/blob/main/files/en-us/learn/javascript/objects/adding_bouncing_balls_features/index.md","last_commit_url":"https://github.com/mdn/content/commit/bc0d0d1ef796435e969f6d65c7e5d3c08f4023aa","filename":"index.md"},"short_title":"Adding features to our bouncing balls demo","parents":[{"uri":"/en-US/docs/Learn","title":"Guides"},{"uri":"/en-US/docs/Learn/JavaScript","title":"JavaScript — Dynamic client-side scripting"},{"uri":"/en-US/docs/Learn/JavaScript/Objects","title":"Introducing JavaScript objects"},{"uri":"/en-US/docs/Learn/JavaScript/Objects/Adding_bouncing_balls_features","title":"Adding features to our bouncing balls demo"}],"pageTitle":"Adding features to our bouncing balls demo - Learn web development | MDN","noIndexing":false}}</script></body></html>