Results 81 - 100 of 885

Details of the object model

JavaScript is an object-based language based on prototypes, rather than being class-based. Because of this different basis, it can be less apparent how JavaScript allows you to create hierarchies of objects and to have inheritance of properties and their values. This chapter attempts to clarify the situation.
Guide Intermediate JavaScript Object

Indexed collections

This chapter introduces collections of data which are ordered by an index value. This includes arrays and array-like constructs such as Array objects and TypedArray objects.
Guide JavaScript Method

Iterators and generators

Processing each of the items in a collection is a very common operation. JavaScript provides a number of ways of iterating over a collection, from simple for loops to map() and filter(). Iterators and Generators bring the concept of iteration directly into the core language and provide a mechanism for customizing the behavior of for...of loops.
Guide Intermediate JavaScript

Loops and iteration

Loops offer a quick and easy way to do something repeatedly. This chapter of the JavaScript Guide introduces the different iteration statements available to JavaScript.
Guide JavaScript Loop Syntax

Meta programming

Starting with ECMAScript 6, JavaScript gains support for the Proxy and Reflect objects allowing you to intercept and define custom behavior for fundamental language operations (e.g. property lookup, assignment, enumeration, function invocation, etc). With the help of these two objects you are able to program at the meta level of JavaScript.
Guide JavaScript Proxy Reflect


This page lists all MDN JavaScript pages along with their summary and tags.
Index JavaScript MDN Meta

Inheritance and the prototype chain

JavaScript is a bit confusing for developers experienced in class-based languages (like Java or C++), as it is dynamic and does not provide a class implementation per se (the class keyword is introduced in ES6, but is syntactical sugar, JavaScript remains prototype-based).
Inheritance Intermediate JavaScript OOP

JavaScript technologies overview

Whereas HTML defines a webpage's structure and content and CSS sets the formatting and appearance, JavaScript adds interactivity to a webpage and creates rich web applications.
Beginner DOM JavaScript

Memory Management

Low-level languages, like C, have low-level memory management primitives like malloc() and free(). On the other hand, JavaScript values are allocated when things (objects, strings, etc.) are created and "automatically" freed when they are not used anymore. The latter process is called garbage collection. This "automatically" is a source of confusion and gives JavaScript (and high-level languages) developers the impression they can decide not to care about memory management. This is a mistake.
JavaScript memory Performance performance

New in JavaScript 1.8.1

The following is a changelog for JavaScript 1.8.1. This version was included in Firefox 3.5.
Firefox 3.5 JavaScript Versions

ECMAScript 5 support in Mozilla

ECMAScript 5.1, an older version of the standard upon which JavaScript is based, was approved in June 2011.
ECMAScript5 JavaScript Versions

ECMAScript 6 support in Mozilla

ECMAScript 2015 (6th Edition) is the current version of the ECMAScript Language Specification standard. Commonly referred to as "ES6", it defines the standard for the JavaScript implementation in SpiderMonkey, the engine used in Firefox and other Mozilla applications.
ECMAScript2015 ECMAScript6 Firefox JavaScript


The constructor method is a special method for creating and initializing an object created with a class.
Classes ECMAScript6 JavaScript


The extends keyword is used in a class declarations or class expressions to create a class with a child of another class.
Classes ECMAScript6 JavaScript


The static keyword defines a static method for a class.
Classes ECMAScript6 JavaScript

Deprecated and obsolete features

This page lists features of JavaScript that are deprecated (that is, still available but planned for removal) and obsolete (that is, no longer usable).
Deprecated JavaScript Obsolete

The legacy Iterator protocol

Firefox, prior to version 26 implemented another iterator protocol that is similar to the standard ES2015 Iterator protocol.
JavaScript Legacy Iterator