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Paradigm Multi-paradigm: prototype-based, functional, imperative
Designed by Brendan Eich, Ecma International
First appeared 1997; 18 years ago (1997)
Typing discipline weak, dynamic
Major implementations
SpiderMonkey, V8, ActionScript, JScript, QtScript, InScript
Influenced by
Self, HyperTalk, AWK, C, Perl, Python, Java, Scheme
Crystal source.png
Filename extensions .es
Internet media type application/ecmascript
Developed by Sun Microsystems,
Ecma International
Initial release June 1997; 18 years ago (1997-06)
Latest release
Edition 6
(June 17, 2015; 5 months ago (2015-06-17))
Type of format Scripting language
Website ECMA-262, ECMA-290,
ECMA-327, ECMA-357,

ECMAScript is a trademarked[1] scripting language specification standardized by Ecma International in ECMA-262 and ISO/IEC 16262. Well-known implementations of the language, such as JavaScript, JScript and ActionScript are widely used for client-side scripting on the Web.


The ECMAScript specification is a standardized specification of a scripting language developed by Brendan Eich of Netscape; initially it was named Mocha, later LiveScript, and finally JavaScript.[2] In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release.[3] In March 1996, Netscape Navigator 2.0 was released, featuring support for JavaScript.

Owing 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 alleviate the Year 2000 problem caused by the JavaScript methods that were based on the Java Date class.[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. Several editions of the language standard have been published since then. 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. Eich commented that "ECMAScript was always an unwanted trade name that sounds like a skin disease."[6]

While both JavaScript and JScript aim to be compatible with ECMAScript, they also provide additional features not described in the ECMA specifications. [7]


There are six editions of ECMA-262 published. Work on version 6 of the standard, codenamed "Harmony", was finalized in June 2015.[8]

Edition Date published Changes from prior 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. Many features proposed for the Fourth Edition have been completely dropped; some are proposed for 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.[9] Pratap Lakshman, Allen Wirfs-Brock
5.1 June 2011 This edition 5.1 of the ECMAScript Standard is fully aligned with third edition of the international standard ISO/IEC 16262:2011. Pratap Lakshman, Allen Wirfs-Brock
6 June 2015[10] The Sixth Edition, known as ECMAScript 2015,[11] adds significant new syntax for writing complex applications, including classes and modules, but defines them semantically in the same terms as ECMAScript 5 strict mode. Other new features include iterators and for/of loops, Python-style generators and generator expressions, arrow functions, binary data, collections (maps, sets and weak maps), and proxies (metaprogramming for virtual objects and wrappers). As the first “ECMAScript Harmony” specification, it is also known as “ES6 Harmony”. Allen Wirfs-Brock
7 Work in progress The Seventh Edition is in a very early stage of development, but is intended to continue the themes of language reform, code isolation, control of effects and library/tool enabling from ES6. New features proposed include promises/concurrency, number and math enhancements, guards and trademarks (an alternative to static typing), operator overloading, value types (first-class number-like objects), new record structures (records, tuples and typed arrays), pattern matching, and traits.[12]

In June 2004, Ecma International published ECMA-357 standard, defining an extension to ECMAScript, known as ECMAScript for XML (E4X). Ecma also defined a "Compact Profile" for ECMAScript – known as ES-CP, or ECMA 327 – that was designed for resource-constrained devices, which was withdrawn in 2015.[13]

4th Edition (abandoned)[edit]

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.[14] An overview of the language was released by the working group on October 23, 2007.[15]

As of August 2008, the ECMAScript 4th edition proposal has been scaled back into a project codenamed ECMAScript Harmony. Features under discussion for Harmony include:

The intent of these features is partly to better support programming in the large, and to allow sacrificing some of the script's ability to be dynamic to improve performance. For example, Tamarin – the virtual machine for ActionScript developed and open sourced by Adobe – has just-in-time compilation (JIT) support for certain classes of scripts.

In addition to introducing new features, some ES3 bugs were proposed to be fixed in edition 4.[16][17] These fixes and others, and support for JSON encoding/decoding, have been folded into the ECMAScript, 5th Edition specification.[18]

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 ECMAScript for XML (E4X) standard. The update has not been without controversy. In late 2007, a debate between Eich, later 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,"[19] and that stakeholders who opposed the changes were being "hidden from view".[20] Eich responded by stating that Wilson seemed to be "repeating falsehoods in blogs" and denied that there was attempt to suppress dissent and challenged critics to give specific examples of incompatibility.[21] 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.[22]

5th Edition[edit]

Yahoo, Microsoft, Google, 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 July 2008: Brendan Eich announced that Ecma TC39 would focus work on the ECMAScript 3.1 (later renamed to ECMAScript, 5th Edition) project with full collaboration of all parties, and vendors would target at least two interoperable implementations by early 2009.[23][24] 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.[25] On December 3, 2009, ECMA-262 5th edition was published.[26]

Harmony, 6th Edition[edit]

In the July 2008 announcement, Eich also stated that the ECMAScript 4 proposal would be superseded by a new project, code-named ECMAScript Harmony. ECMAScript Harmony names the agreed upon design trajectory of post-ES5 editions. It 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).[27]

Drafts of have been published periodically since July 2011,[28] and was finalized in June 2015.[8]


The ECMAScript language includes structured, dynamic, functional, and prototype-based features.[29]


Main article: ECMAScript syntax


ECMAScript is supported in many applications, especially Web browsers, where it is implemented by JavaScript, or, in the case of Internet Explorer, JScript. Implementations sometimes include extensions to the language, or to the standard library and related application programming interfaces (API) such as the World Wide Web Consortium (W3C) specified Document Object Model (DOM). This means that applications written in one implementation may be incompatible with another, unless they are written to use only a common subset of supported features and APIs.

Implementation Applications ECMAScript edition
SpiderMonkey Firefox, the Gecko layout engine, Adobe Acrobat[d 1] ECMA-262, edition 5.1, and features from upcoming 6 and 7[d 2]
Rhino Java Platform, Standard Edition
V8 Google Chrome, Node.js, Opera ECMA-262, edition 5.1, and features from upcoming 6[d 3][d 4]
JavaScriptCore (Nitro) WebKit, Safari, Qt 5 ECMA-262, edition 5.1
JScript 9.0 Internet Explorer, the Trident layout engine ECMA-262, edition 5.1
Nashorn Java ECMA-262, edition 5.1[d 5]
Carakan (deprecated) Opera 12 ECMA-262, edition 5[d 6][d 7]
RemObjects Script for .NET ECMA-262, edition 5
KJS KHTML ECMA-262, edition 5.1[d 8] and features from upcoming 6[d 9]
Ejscript Appweb Web Server, Samba 4 ECMA-262, edition 3[d 10]
JScript .NET Microsoft .NET Framework ECMA-262, edition 3[d 11]
ActionScript Adobe Flash, Adobe Flex, Adobe AIR ECMA-262, edition 4[d 12][d 13]
Adobe ExtendScript Adobe Creative Suite products: InDesign, Illustrator, Photoshop,
Bridge, After Effects, Premiere Pro
ECMA-262, edition 3[citation needed]
DMDScript ECMA-262
CriScript ECMA-262, edition 3
InScript iCab ECMA-262, edition 3
Max/MSP engine Max/MSP ECMA-262, edition 3
Galio engine Galio ECMA-262, edition 3
QtScript (deprecated) KDE SC 4 ECMA-262, edition 3
Caja ECMA-262, edition 3[d 14]
Chakra Microsoft Edge ECMA-262, edition 5.1, and features from upcoming 6[d 15]
  1. ^ Adobe Acrobat 9.0 uses the SpiderMonkey 1.7 engine: JavaScript for Acrobat API Reference
  2. ^ SpiderMonkey already supports a wide range of upcoming features: ECMAScript 6 support in Mozilla and ECMAScript 7 support in Mozilla
  3. ^ V8, the JavaScript engine created by Google and used in Chrome, implements ECMAScript as specified in ECMA-262, 5th edition: V8 JavaScript Engine.
  4. ^ Chrome also implements non-ECMAScript-standard extensions to the language that are present in WebKit, in order to maintain compatibility with JavaScriptCore : V8 JavaScript Engine issue tracker.
  5. ^ Full ECMAScript 5.1 support in Opera 11.51+[1].
  6. ^ Full ECMAScript 5.1 support in Opera 11.51+[2].
  7. ^ Opera's implementation includes some JavaScript and JScript extensions: ECMAScript support in Opera Presto 2.3
  8. ^ "bUscher  » Blog Archive  » kjs finally under 1000 fails!". 
  9. ^ Commits marked with ES6 are implementations of ES6 features:
  10. ^ This implementation asserts to support some extensions proposed in drafts of ECMAScript edition 4 (and now ECMAScript Harmony): Ejscript Overview.
  11. ^ 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.
  12. ^ Completely conforming implementation of the ECMAScript fourth edition draft specification: ActionScript
  13. ^ 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.
  14. ^ Caja emulates strict mode as specified in the ECMAScript edition 5 draft.
  15. ^ Microsoft states that Edge "supports most ES2015 features," supporting 81% of the specification as of May 2015 and 67% as of September 2015. [3][4]

Version correspondence[edit]

The following table is based on tedster's history compilation forum post[30] and Microsoft's JScript version information Webpage.[31] 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: ECMAScript for XML (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)[32]
JavaScript 2.0 (Work in progress) Harmony (Work in progress; see the section "ECMAScript Harmony").

Conformance tests[edit]

In 2010, Ecma International started developing a standards test for Ecma 262 ECMAScript.[33] Test262 is an ECMAScript conformance test suite that can be used to check how closely a JavaScript implementation follows the ECMAScript 5th Edition Specification. The test suite contains thousands of individual tests, each of which tests some specific requirements of the ECMAScript specification.

Development of test262 is a project of Ecma Technical Committee 39 (TC39). The testing framework and individual tests are created by member organizations of TC39 and contributed to Ecma for use in Test262.

Important contributions were made by Google (Sputnik testsuite) and Microsoft who both contributed thousands of tests. The Test262 testsuite already contains more than 11,000 tests and is being developed further as of 2013.

The following table shows current conformance results of browser products. Lower scores are better, although scores can not be compared, as tests are not weighted. Also, be aware that Test262 itself is likely to contain bugs that may impact a browser's score. So browsers with a score significantly lower than the current test suite bug count may not necessarily do better than those with a higher one.[34] That may be particularly true when several browsers have a higher score in their current development builds as compared to their last released version.

Results of test262 (suite version: ES5, suite date: 2014-09-18)
Product Latest Stable Test262 failed Preview/Beta Test262 failed Alpha Test262 failed Nightly Test262 failed
Google Chrome 46.0.2490.86 m 207/11552 47.0.2526.69 beta-m 208/11552 48.0.2564.10 dev-m 203/11552 48.0.2569.0 canary 203/11552
Mozilla Firefox 42.0 260/11552 43.0 Beta 5 260/11552 44.0a2 (20151120004044) 260/11552 45.0a1 (20151120030227) 260/11552
ESR 38.4.0 228/11552
Internet Explorer 11.0.25 (11.0.9600.18097) 8/11552
Maxthon 18/11552
Opera 33.0.1990.115 207/11552 beta 34.0.2036.3 208/11552 developer 35.0.2052.0 210/11552
12.17 (classic) 11/11552
Safari 7.1 (9537.85) 7/11552

See also[edit]


  1. ^ "TC39 - ECMAScript® (formerly TC39-TG1)". Ecma International. Retrieved 22 August 2015. 
  2. ^ Krill, Paul (2008-06-23). "JavaScript creator ponders past, future | Developer World". InfoWorld. Retrieved 2013-10-31. 
  3. ^ "Press Release". Archived from the original on 2007-09-16. Retrieved 2013-10-31. 
  4. ^ "Brendan's Roadmap Updates: Popularity". Archived from the original on 17 May 2008. 
  5. ^ "Press Release". Archived from the original on 1998-12-03. Retrieved 2013-10-31. 
  6. ^ "Will there be a suggested file suffix for es4?". 2006-10-03. Retrieved 2013-10-31. 
  7. ^ "JScript VS JavaScript". 25-11-2015.  Check date values in: |date= (help)
  8. ^ a b [5]. EMCAScript. Retrieved on 2015-06-19.
  9. ^ "Changes to JavaScript, Part 1: EcmaScript 5". YouTube. 2009-05-18. Retrieved 2013-10-31. 
  10. ^
  11. ^
  12. ^ "strawman:strawman [ES Wiki]". 2013-09-18. Retrieved 2013-10-31. 
  13. ^ 2015-03-24 Meeting Notes. ESDiscuss. Also see Ecma withdrawn Standards. ECMA.
  14. ^ "ES4 overview paper released". Retrieved 2013-10-31. 
  15. ^ "Proposed ECMAScript 4th Edition – Language Overview" (PDF). 23 October 2007. 
  16. ^ John Resig. "John Resig – Bug Fixes in JavaScript 2". Retrieved 2013-10-31. 
  17. ^ "Compatibility Between ES3 and Proposed ES4" (PDF). Retrieved 2013-10-31. 
  18. ^
  19. ^ "ECMAScript 3 and Beyond – IEBlog – Site Home – MSDN Blogs". 2007-10-30. Retrieved 2013-10-31. 
  20. ^ "What I think about ES4. - Albatross! - Site Home – MSDN Blogs". 2007-10-31. Retrieved 2013-10-31. 
  21. ^ "Open letter to Chris Wilson". Brendan Eich. 2007-10-31. Retrieved 2013-10-31. 
  22. ^ "JavaScript 2 and the Open Web". 2007-11-20. Retrieved 2014-01-20. 
  23. ^ "ECMAScript Harmony". Retrieved 2013-10-31. 
  24. ^ "A Major Milestone in JavaScript Standardization – JScript Blog – Site Home – MSDN Blogs". 2009-04-09. Retrieved 2013-10-31. 
  25. ^ "Ecma International finalises major revision of ECMAScript". Ecma International. 2009-04-09. Retrieved 2009-05-22. 
  26. ^ "Ecma latest news". Retrieved 2013-10-31. 
  27. ^ John Resig. "John Resig – ECMAScript Harmony". Retrieved 2013-10-31. 
  28. ^ harmony:specification_drafts [ES Wiki]. Retrieved on 2013-10-23.
  29. ^ "About". ECMAScript. Retrieved 2009-12-17. 
  30. ^ "JavaScript – JScript – ECMAScript version history". Retrieved 2009-12-17. 
  31. ^ "Version Information (JScript)". Archived from the original on 2009-12-17. Retrieved 2009-12-17. 
  32. ^ "Introducing JScript .NET". Retrieved 2010-01-12. 
  33. ^ "ECMAScript Language – test262". Retrieved 2013-10-31. 
  34. ^ Schuster, Tom. "Bug 1453". bug database. Retrieved 12 October 2014. 

External links[edit]

ISO Standard
Ecma Standards