New in JavaScript

This chapter contains information about JavaScript's version history and implementation status for Mozilla/SpiderMonkey-based JavaScript applications, such as Firefox.

ECMAScript versions

Language resources

Learn more about the ECMAScript standards on which the JavaScript language is based on.

ECMAScript 5 support

Implementation status for the current standard ECMA-262 Edition 5.1 in Mozilla-based engines and products.

ECMAScript 6 support

Implementation status for the draft ECMA-262 Edition 6 in Mozilla-based engines and products.

ECMAScript 7 support

Implementation status for the upcoming ECMA-262 Edition 7 in Mozilla-based engines and products.

JavaScript release notes

Firefox JavaScript changelog

See this changelog for JavaScript features implemented in Firefox 5 and later.

Chrome JavaScript changelog

(TODO). See this changelog for JavaScript features implemented in Chrome releases.

JavaScript versions

Deprecated ( ). The explicit versioning and opt-in of language features was Mozilla-specific and is in process of being removed. Firefox 4 was the last version which referred to an JavaScript version (1.8.5). With new ECMA standards, JavaScript language features are now often mentioned with their initial definition in ECMA-262 Editions such as Edition 6 (ES6).

JavaScript was released as version 1.0 in March 1996 in Netscape Navigator 2.0 and Internet Explorer 2.0.

JavaScript 1.1

Version shipped in Netscape Navigator 3.0. Released on August 19, 1996.

JavaScript 1.2

Version shipped in Netscape Navigator 4.0-4.05. Released on June 11, 1997.

JavaScript 1.3

Version shipped in Netscape Navigator 4.06-4.7x. Released on October 19, 1998.
Standardization work to be compliant with ECMA-262 1st and 2nd Edition.

JavaScript 1.4

Version shipped in Netscape's server side JavaScript. Released in 1999.

JavaScript 1.5

Version shipped in Netscape Navigator 6.0 and Firefox 1.0. Release on November 14, 2000.
Standardization work to be compliant with ECMA-262 3rd Edition.

JavaScript 1.6

Version shipped in Firefox 1.5. Released in November 2005.
Includes ECMAScript for XML (E4X), new Array methods plus String and Array generics.

JavaScript 1.7

Version shipped in Firefox 2. Released in October 2006.
Includes generators, iterators, array comprehensions, let expressions, and destructuring assignment.

JavaScript 1.8

Version shipped in Firefox 3. Released in June 2008.
Includes expression closures, generator expressions and Array.reduce()

JavaScript 1.8.1

Version shipped in Firefox 3.5. Released on June 30, 2009.
Includes the TraceMonkey JIT and supports native JSON.

JavaScript 1.8.2

Version shipped in Firefox 3.6. Released June 22, 2009.
Includes only minor changes.

JavaScript 1.8.5

Version shipped in Firefox 4. Released July 27, 2010.
Includes many new features for ECMA-262 Edition 5 compliance.
This is the last JavaScript version.

Features still requiring version opt-in

let statement

The let statement requires the JavaScript version 1.7 (or higher) opt-in. See bug 932517 and bug 932513.