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JavaScript (JS) is a lightweight interpreted (or just-in-time compiled) programming language with first-class functions. While it is most well-known as the scripting language for Web pages, many non-browser environments also use it, such as Node.js, Apache CouchDB and Adobe Acrobat. JavaScript is a prototype-based, multi-paradigm, single-threaded, dynamic language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles.
JavaScript's dynamic capabilities include runtime object construction, variable parameter lists, function variables, dynamic script creation (via eval), object introspection (via for...in and Object utilities), and source-code recovery (JavaScript functions store their source text and can be retrieved through toString()).
This section is dedicated to the JavaScript language itself, and not the parts that are specific to Web pages or other host environments. For information about APIs that are specific to Web pages, please see Web APIs and DOM.
The standards for JavaScript are the ECMAScript Language Specification (ECMA-262) and the ECMAScript Internationalization API specification (ECMA-402). As soon as one browser implements a feature, we try to document it. This means that cases where some proposals for new ECMAScript features have already been implemented in browsers, documentation and examples in MDN articles may use some of those new features. Most of the time, this happens between the stages 3 and 4, and is usually before the spec is officially published.
Do not confuse JavaScript with the Java programming language — JavaScript is not "Interpreted Java". Both "Java" and "JavaScript" are trademarks or registered trademarks of Oracle in the U.S. and other countries. However, the two programming languages have very different syntax, semantics, and use.
JavaScript documentation of core language features (pure ECMAScript, for the most part) includes the following:
For complete beginners
Head over to our Learning Area JavaScript topic if you want to learn JavaScript but have no previous experience with JavaScript or programming. The complete modules available there are as follows: JavaScript first steps\t Answers some fundamental questions such as "what is JavaScript?", "what does it look like?", and "what can it do?", along with discussing key JavaScript features such as variables, strings, numbers, and arrays. JavaScript building blocks\t Continues our coverage of JavaScript's key fundamental features, turning our attention to commonly-encountered types of code blocks such as conditional statements, loops, functions, and events. Introducing JavaScript objects\t The object-oriented nature of JavaScript is important to understand if you want to go further with your knowledge of the language and write more efficient code, therefore we've provided this module to help you. Asynchronous JavaScript\t Discusses asynchronous JavaScript, why it is important, and how it can be used to effectively handle potential blocking operations such as fetching resources from a server. Client-side web APIs\t Explores what APIs are, and how to use some of the most common APIs you'll come across often in your development work.
JavaScript guide
JavaScript Guide\t A much more detailed guide to the JavaScript language, aimed at those with previous programming experience either in JavaScript or another language.
Intermediate
Understanding client-side JavaScript frameworks\t JavaScript frameworks are an essential part of modern front-end web development, providing developers with proven tools for building scalable, interactive web applications. This module gives you some fundamental background knowledge about how client-side frameworks work and how they fit into your toolset, before moving on to a series of tutorials covering some of today's most popular ones. JavaScript language overview\t An overview of the basic syntax and semantics of JavaScript for those coming from other programming languages to get up to speed. JavaScript data structures\t Overview of available data structures in JavaScript. Equality comparisons and sameness\t JavaScript provides three different value comparison operations: strict equality using ===, loose equality using ==, and the Object.is() method. Enumerability and ownership of properties\t How different methods that visit a group of object properties one-by-one handle the enumerability and ownership of properties. Closures\t A closure is the combination of a function and the lexical environment within which that function was declared.
Browse the complete JavaScript reference documentation.
Standard objects\t
Get to know standard built-in objects Array, Boolean, Date, Error, Function, JSON, Math, Number, Object, RegExp, String, Map, Set, WeakMap, WeakSet, and others.
Expressions and operators\t
Learn more about the behavior of JavaScript's operators instanceof, typeof, new, this, the operator precedence, and more.
Statements and declarations\t
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MDN Web Docs, previously Mozilla Developer Network and formerly Mozilla Developer Center, is a documentation repository and learning resource for web developers. It was started by Mozilla in 2005 as a unified place for documentation about open web standards, Mozilla's own projects, and developer guides.
Feb 1, 2020 · MDN Web Docs is a wiki that covers HTML5, CSS, JavaScript, Web APIs, graphics, mathML, and web assembly. Learn how to use MDN Web Docs to find the information you need to build projects on the open Web.
Jun 11, 2020 · Learn the basics of front-end web development with the Front-end developer learning pathway (FED learning pathway), a structured and opinionated guide to HTML, CSS, JavaScript, web forms, testing, accessibility, and modern client-side tooling. The FED learning pathway covers the essentials of web development, provides clear direction and assessments, and includes links to more advanced resources on MDN Web Docs.
Nov 24, 2022 · MDN Web Docs. This page contains planning, process, and team info about MDN Web Docs. Questions about MDN? Reach out on the MDN discussion forum!
