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Paradigm Multi-paradigm: prototype-based, functional, imperative, scripting
Appeared in 1997
Designed by Brendan Eich, Ecma International
Typing discipline duck, weak, dynamic
Dialects JavaScript, ActionScript, JScript, QtScript, DMDScript, InScript
Influenced by Self, HyperTalk, AWK, C, Perl, Python, Java
<tr class=""><th style="text-align:left; ">Internet media type</th>
   <td class="" style="">application/ecmascript[1]</td></tr><tr class=""><th style="text-align:left; ">Developed by</th>
   <td class="" style="">Sun Microsystems,
Ecma International</td></tr><tr class=""><th style="text-align:left; ">Initial release</th> <td class="" style="">June 1997</td></tr><tr class=""><th style="text-align:left; ">Latest release</th> <td class="" style="">Edition 5 / December 2009</td></tr><tr class=""><th style="text-align:left; ">Type of format</th> <td class="" style="">Scripting language</td></tr><tr class=""><th style="text-align:left; ">Extended from</th> <td class="" style="">JavaScript</td></tr><tr class=""><th style="text-align:left; ">Website</th> <td class="" style="">ECMA-262, ECMA-290,
ECMA-327, ECMA-357</td></tr>


File:Crystal source.png
Filename extension <code>.es</code>
This article is part of

the JavaScript series.

JavaScript syntax
JavaScript topics

ECMAScript is a scripting language, standardized by Ecma International in the ECMA-262 specification and ISO/IEC 16262. The language is widely used on the web, especially in the form of its three best-known dialects, JavaScript, ActionScript, and JScript.



JavaScript was originally developed by Brendan Eich of Netscape under the name Mocha, later LiveScript, and finally renamed to JavaScript.[2] In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release.[3] In March 1996, Netscape Navigator 2.0 was out, featuring support for JavaScript.

Due to the widespread success of JavaScript as a client-side scripting language for web pages, Microsoft developed a compatible dialect of the language, naming it JScript to avoid trademark issues. JScript added new date methods to fix the non-Y2K-friendly methods in JavaScript, which were based on java.util.Date.[4] JScript was included in Internet Explorer 3.0, released in August 1996.

Netscape delivered JavaScript to Ecma International for standardization and the work on the specification, ECMA-262, began in November 1996.[5] The first edition of ECMA-262 was adopted by the Ecma General Assembly of June 1997.[6]

ECMAScript is the name of the scripting language standardized in ECMA-262. Both JavaScript and JScript aim to be compatible with ECMAScript, while providing additional features not described in the Ecma specification.

The name "ECMAScript" was a compromise between the organizations involved in standardizing the language, especially Netscape and Microsoft, whose disputes dominated the early standards sessions. Brendan Eich, the creator of JavaScript, is on record as saying that "ECMAScript was always an unwanted trade name that sounds like a skin disease."[7]


There are four editions of ECMA-262 published. Work on a future edition codenamed "Harmony", is in progress.

Edition Date published Differences to the previous edition Editor
1 June 1997 First edition Guy L. Steele, Jr.
2 June 1998 Editorial changes to keep the specification fully aligned with ISO/IEC 16262 international standard Mike Cowlishaw
3 December 1999 Added regular expressions, better string handling, new control statements, try/catch exception handling, tighter definition of errors, formatting for numeric output and other enhancements Mike Cowlishaw
4 Abandoned Fourth Edition was abandoned, due to political differences concerning language complexity, with some of the work forming the basis of Fifth Edition and some forming the basis of ECMAScript Harmony.
5 December 2009 Adds "strict mode", a subset intended to provide more thorough error checking and avoid error-prone constructs. Clarifies many ambiguities in the 3rd edition specification, and accommodates behaviour of real-world implementations that differed consistently from that specification. Adds some new features, such as getters and setters, library support for JSON, and more complete reflection on object properties.[8] Pratap Lakshman, Allen Wirfs-Brock
Harmony Work in progress Multiple new concepts and language features — see the section "Future development" below.

In June 2004, Ecma International published ECMA-357 standard, defining an extension to ECMAScript, known as E4X (ECMAScript for XML).

Ecma also defined a "Compact Profile" for ECMAScript — known as ES-CP, or ECMA 327 — which is designed for resource-constrained devices. Several of the dynamic features of ECMAScript (such as the "eval" function) are made optional, thus allowing the runtime to make more assumptions about the behaviour of programs and therefore make more performance trade-offs when running the code. The HD DVD standard was one place where the ECMAScript Compact Profile was used in favour of full ECMAScript in order to reduce processing and memory requirements on a device.


The ECMAScript language includes structured, dynamic, functional, and prototype-based features, as officially summarized here.[9]



ECMAScript is supported in many applications, especially web browsers, where it is commonly called JavaScript. Dialects sometimes include extensions to the language, or to the standard library and related APIs such as the W3C-specified DOM. This means that applications written in one dialect may be incompatible with another, unless they are written to use only a common subset of supported features and APIs.

Note that there is a distinction between a dialect and an implementation. A dialect of a language is significant variation of the language, while an implementation of a language/dialect executes a program written in that dialect.

Application/Implementation Dialect and latest version ECMAScript edition
Mozilla Firefox, the Gecko layout engine, SpiderMonkey, and Rhino[d 1] JavaScript 1.8.1[d 2] ECMA-262, edition 3
Google Chrome, the V8 engine JavaScript[d 2] ECMA-262, edition 3[d 3]
Internet Explorer, the Trident layout engine JScript 5.8 ECMA-262, edition 3
Opera ECMAScript[d 4] ECMA-262, edition 3
KHTML layout engine, KDE's Konqueror, and Apple Inc.'s Safari[d 5] JavaScript[d 2] ECMA-262, edition 3</sup>
Appweb Web Server, Samba 4 Ejscript 0.9.9 ECMA-262, edition 3[d 6]
Microsoft .NET Framework JScript .NET 8.0 ECMA-262, edition 3[d 7]
Adobe Flash and Adobe Flex ActionScript 3 ECMA-262, edition 3[d 8]
Adobe Acrobat JavaScript 1.7[d 9] ECMA-262, edition 3
General purpose scripting language DMDScript 1.15 ECMA-262
OpenLaszlo Platform JavaScript[d 10] ECMA-262, edition 3[d 11]
CriScript, JScript for game platforms CriScript 0.91.0 ECMA-262, edition 3
iCab InScript 3.22 (abandoned) ECMA-262, edition 3
Max/MSP JavaScript 1.5[d 2] ECMA-262, edition 3
ANT Galio 3 JavaScript 1.5[d 2][d 12] ECMA-262, edition 3
KDE QtScript ECMA-262, edition 3
Caja ECMA-262, edition 3[d 13]
Objective-J ECMA-262, edition 3
WMLScript ECMA-262, edition 3
  1. The Mozilla implementations, (SpiderMonkey in the C programming language and Rhino in the Java programming language), are used in several third-party programs, including the Yahoo! Widget Engine (Konfabulator) and the Macintosh system-level scripting language JavaScript OSA.
  2. 2.0 2.1 2.2 2.3 2.4 Mozilla manages the official version of JavaScript. Most non-Mozilla implementations claiming JavaScript "compliance" do not actually support most JavaScript extensions; rather, they target ECMA-262, edition 3.
  3. V8 implements ECMAScript as specified in ECMA-262, 3rd edition: V8 JavaScript Engine.
  4. Opera's implementation includes some JavaScript and JScript extensions: ECMAScript support in Opera Presto 2.3
  5. Apple's Safari uses JavaScriptCore which is based on the KDE KJS library.
  6. This implementation asserts to support some extensions proposed in drafts of ECMAScript edition 4 (and now ECMAScript Harmony): Ejscript Overview.
  7. Microsoft asserts that JScript 8.0 supports "almost all of the features of the ECMAScript Edition 3 Language Specification" but does not list the unsupported features.
  8. In addition to supporting ECMA-262 edition 3, ActionScript 3 also included support for extensions proposed in drafts of ECMAScript edition 4: The Kiwi Project: AS3 language 101 for C/C++ coders.
  9. Adobe Acrobat 9.0 uses the SpiderMonkey 1.7 engine: JavaScript for Acrobat API Reference
  10. OpenLaszlo both uses an ECMAScript dialect as noted in the Developer's Guide: Appendix B: ECMAScript and can compile down to JavaScript targeted for the browser (the DHTML target).
  11. As of version 4, OpenLaszlo implements standard ECMAScript edition 3 with some extensions proposed in drafts of ECMAScript edition 4: OpenLaszlo 4.
  12. ANT Galio Browser claims support for JavaScript 1.5.
  13. Caja emulates strict mode as specified in the ECMAScript edition 5 draft.

Version correspondence

The following table is based on [10] and;[11] items on the same line are approximately the same language.

JavaScript JScript ECMAScript
1.0 (Netscape 2.0, March 1996) 1.0 (IE 3.0 - early versions, August 1996)
1.1 (Netscape 3.0, August 1996) 2.0 (IE 3.0 - later versions, January 1997)
1.2 (Netscape 4.0-4.05, June 1997)
1.3 (Netscape 4.06-4.7x, October 1998) 3.0 (IE 4.0, Oct 1997) Edition 1 (June 1997) / Edition 2 (June 1998)
1.4 (Netscape Server only) 4.0 (Visual Studio 6, no IE release)
5.0 (IE 5.0, March 1999)
5.1 (IE 5.01)
1.5 (Netscape 6.0, Nov 2000; also
later Netscape and Mozilla releases)
5.5 (IE 5.5, July 2000) Edition 3 (December 1999)
5.6 (IE 6.0, October 2001)
1.6 (Gecko 1.8, Firefox 1.5, November 2005) Edition 3, with some compliant enhancements: E4X, Array extras (e.g. Array.prototype.forEach), Array and String generics (New in JavaScript 1.6)
1.7 (Gecko 1.8.1, Firefox 2, October 2006) Edition 3 plus all JavaScript 1.6 enhancements, plus Pythonic generators and array comprehensions ([a*a for (a in iter)]), block scope with let, destructuring assignment (var [a,b]=[1,2]) (New in JavaScript 1.7)
1.8 (Gecko 1.9, Firefox 3, June 2008) Edition 3 plus all JavaScript 1.7 enhancements, plus expression closures (function(x) x * x), generator expressions, and more (New in JavaScript 1.8)
JScript .NET (ASP.NET; no IE release) (JScript .NET is said to have been designed with the participation of other Ecma members[12])
JavaScript 2.0 (Work in progress) Harmony (Work in progress; see the section "ECMAScript Harmony" below).

Future development

The proposed fourth edition of ECMA-262 (ECMAScript 4 or ES4) would have been the first major update to ECMAScript since the third edition was published in 1999. The specification (along with a reference implementation) was originally targeted for completion by October 2008.[13] An overview of the language was released by the working group on October 22, 2007.

As of August 2008, the ECMAScript 4th edition proposal has been scaled back into a project codenamed ECMAScript Harmony.


Features under discussion for a future edition (originally "ECMAScript 4"; now ECMAScript Harmony) include:

The intent of these features is partly to better support "programming in the large", and to let programmers sacrifice some of the script's ability to be dynamic for performance. For example, Tamarin — the virtual machine for ActionScript developed and open sourced by Adobe — has JIT compilation support for certain classes of scripts.

Bug fixes and backwards compatibility

In addition to introducing new features, some ES3 bugs were proposed to be fixed in edition 4.[14][15] These fixes and others, and support for JSON encoding/decoding, have been folded into the ECMAScript, 5th Edition specification.[16]


Work started on Edition 4 after the ES-CP (Compact Profile) specification was completed, and continued for approximately 18 months where slow progress was made balancing the theory of Netscape's JavaScript 2 specification with the implementation experience of Microsoft's JScript .NET. After some time, the focus shifted to the E4X standard.

The update has not been without controversy. In late 2007, a debate between Eich, now the Mozilla Foundation's CTO, and Chris Wilson, Microsoft's platform architect for Internet Explorer, became public on a number of blogs. Wilson cautioned that because the proposed changes to ECMAScript made it backwards incompatible in some respects to earlier versions of the language, the update amounted to "breaking the Web,"[17] and that stakeholders who opposed the changes were being "hidden from view".[18] Eich responded by stating that Wilson seemed to be "repeating falsehoods in blogs" and denied that there was attempt to suppress dissent and challenging critics to give specific examples of incompatibility.[19] He also pointed out that Microsoft Silverlight and Adobe AIR rely on C# and ActionScript 3 respectively, both of which are larger and more complex than ECMAScript Edition 3.[20]

ECMAScript, 5th Edition

Microsoft, Yahoo, and other 4th edition dissenters formed their own subcommittee to design a less ambitious update of ECMAScript 3, tentatively named ECMAScript 3.1. This edition would focus on security and library updates with a large emphasis on compatibility. After the aforementioned public sparring, the ECMAScript 3.1 and ECMAScript 4 teams agreed on a compromise: the two editions would be worked on in parallel, with coordination between the teams to ensure that ECMAScript 3.1 remains a strict subset of ECMAScript 4 in both semantics and syntax.

However, the differing philosophies in each team resulted in repeated breakages of the subset rule, and it remained doubtful that the ECMAScript 4 dissenters would ever support or implement ECMAScript 4 in the future. After over a year since the disagreement over the future of ECMAScript within the Ecma Technical Committee 39, the two teams reached a new compromise in August 2008: Ecma TC39 announced it would focus work on the ECMAScript 3.1 (later renamed to ECMAScript, 5th Edition) project with full collaboration of all parties, and it would target two interoperable implementations by early 2009.[21][22] In April 2009, Ecma TC39 published the "final" draft of the 5th edition and announced that testing of interoperable implementations was expected to be completed by mid-July.[23] On December 3, 2009, ECMA-262 5th edition was published.[24]

ECMAScript Harmony

In the same announcement, Ecma TC39 also stated that the ECMAScript 4 proposal would be superseded by a new project, code-named ECMAScript Harmony. ECMAScript Harmony will include syntactic extensions, but the changes will be more modest than ECMAScript 4 in both semantic and syntactic innovation. Packages, namespaces and early binding from ECMAScript 4 are no longer included for planned releases. In addition, other goals and ideas from ECMAScript 4 are being rephrased to keep consensus in the committee; these include a notion of classes based on ECMAScript, 5th Edition (being an update to ECMAScript, 3rd edition).[25] As of December 2009, there is no publicly announced release date for ECMAScript Harmony. Depending on Ecma, Harmony may end up being called ECMAScript, 6th edition.

See also


  1. RFC 4329
  2. InfoWorld: JavaScript creator ponders past, future
  3. JavaScript Press Release
  4. Brendan's Roadmap Updates: Popularity
  5. JavaScript Standardization Press Release
  6. ECMAScript 3rd Edition specification
  7. es4-discuss: Will there be a suggested file suffix for es4?
  8. Changes to JavaScript, Part 1: EcmaScript 5
  9. "About". ECMAScript. Retrieved 2009-12-17. 
  10. "JavaScript - JScript - ECMAScript version history". Retrieved 2009-12-17. 
  11. "Version Information (JScript)". Retrieved 2009-12-17. 
  12. "Introducing JScript .NET". Retrieved 2010-01-12. 
  13. es4-discuss: ES4 overview paper released
  14. John Resig - Bug Fixes in JavaScript 2
  15. Incompatibilities between ES3 and ES4
  16. [1][dead link]
  17. IEBlog: ECMAScript 3 and Beyond
  18. Albatross!: What I think about ES4
  19. Brendan's Roadmap Updates: Open letter to Chris Wilson
  20. Brendan's Roadmap Updates: My @media Ajax Keynote
  21. ECMAScript Harmony announcement
  22. Announcement of the 5th edition candidate by the specification editors
  23. "Ecma International finalises major revision of ECMAScript". Ecma International. 2009-04-09. Retrieved 2009-05-22. 
  24. Ecma News: 98th General Assembly approved documents
  25. John Resig: ECMAScript Harmony

External links

Template:Ecma International Standards Template:ISO standardsca:ECMAScript da:ECMAScript es:ECMAScript fr:ECMAScript ko:ECMA스크립트 hu:ECMAScript ja:ECMAScript no:ECMAScript pl:ECMAScript pt:ECMAScript ru:ECMAScript sv:Ecmascript th:ECMAScript uk:ECMAScript zh:ECMAScript

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