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JavaScript (JS) is a programming language and core technology of the Web, alongside HTML and CSS. It was created by Brendan Eich in 1995. As of 2025, the overwhelming majority of websites (98.9%) uses JavaScript for client side webpage behavior.

AI overview

JavaScript is a programming language that powers interactive features on nearly all websites today, making it one of the most essential technologies for how the internet works. It was created by Brendan Eich in 1995 and remains fundamental to web development alongside HTML and CSS, with 98.9% of websites currently using it.

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Key facts

Programming language.name: JavaScript
Programming language.screenshot: JavaScript code.png
Programming language.screenshot caption: Screenshot of JavaScript source code
Programming language.paradigms: Multi-paradigm: event-driven, functional, imperative, procedural, object-oriented
Programming language.memory management: Garbage collected
Programming language.family: ECMAScript
Programming language.designers: Brendan Eich of Netscape first; then others contributed to ECMAScript standard
Programming language.typing: Dynamic, weak, duck
Programming language.scope: lexical
Programming language.file extensions: .js • .mjs • .cjs
Programming language.implementations: V8, JavaScriptCore, SpiderMonkey;Chakra (deprecated)

Article

57 sections

Contents

History
Creation at Netscape
Adoption by Microsoft
The rise of JScript
Growth and standardization
Reaching maturity
Trademark
Website client-side usage
Examples of scripted behavior
Libraries and frameworks
Other usage{{anchor|Server-side_JavaScript|Uses_outside_web_pages}}
Execution
JavaScript engine
Runtime system
Features
Imperative and structured
Weakly typed
Dynamic
Typing
Run-time evaluation
Object-orientation (prototype-based)
Prototypes
Functions as object constructors
Functions as methods
Functional
Lexical closure
Anonymous function
Delegative
Functions as roles (Traits and Mixins)
Object composition and inheritance
Miscellaneous
Zero-based numbering
Variadic functions
Array and object literals
Regular expressions
Promises
Async/await
Vendor-specific extensions
Syntax
Security
Cross-site scripting
Cross-site request forgery
Misplaced trust in the client
Misplaced trust in developers
Browser and plugin coding errors
Sandbox implementation errors
Hardware vulnerabilities
Development tools
Related technologies
Java
JSON
Transpilers
WebAssembly
Notes
References
Further reading
External links

Web browsers have a dedicated JavaScript engine that executes the client code. These engines are also utilized in some servers and a variety of apps. The most popular runtime system for non-browser usage is Node.js.