ECMAScript 5
Crystal source.png
Filename extensions .es
Internet media type application/ecmascript
Developed by Sun Microsystems,
Ecma International
Initial release June 1997; 20 years ago (1997-06)
Latest release
Edition 8
(June 2017; 8 months ago (2017-06))
Type of format Scripting language
Website ECMA-262, ECMA-290,
ECMA-327, ECMA-357,

ECMAScript (or ES)[1] is a trademarked[2]scripting-language specification standardized by Ecma International in ECMA-262 and ISO/IEC 16262. It was created to standardize JavaScript, so as to foster multiple independent implementations. JavaScript has remained the best-known implementation of ECMAScript since the standard was first published, with other well-known implementations including JScript and ActionScript.[3] Coders commonly use ECMAScript for client-side scripting on the World Wide Web, and it is increasingly being used for writing server applications and services using Node.js.


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.[4] In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release.[5] 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.[6] 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.[7] The first edition of ECMA-262 was adopted by the Ecma General Assembly in 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."[8]

While both JavaScript and JScript aim to be compatible with ECMAScript, they also provide additional features not described in the ECMA specifications.[9]


There are eight editions of ECMA-262 published. Work on version 8 of the standard was finalized in June 2017.[10]

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.[11] 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[12] The Sixth Edition, initially known as ECMAScript 6 (ES6) and later renamed to ECMAScript 2015 (ES2015)[12] 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, typed arrays, collections (maps, sets and weak maps), promises, number and math enhancements, reflection, 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 June 2016[13] The Seventh Edition, also known as ECMAScript 2016,[13] intended to continue the themes of language reform, code isolation, control of effects and library/tool enabling from ES2015, includes two new features: the exponentiation operator (**) and Array.prototype.includes. Brian Terlson
8 June 2017[10] New features proposed include concurrency and atomics, zero-copy binary data transfer, more number and math enhancements, syntactic integration with promises (await/async), observable streams, SIMD types, better metaprogramming with classes, class and instance properties, operator overloading, value types (first-class primitive-like objects), records and tuples, and traits.[14][15]

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.[16]

4th Edition (abandoned)

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.[17] An overview of the language was released by the working group on October 23, 2007.[18]

By August 2008, the ECMAScript 4th edition proposal had been scaled back into a project codenamed ECMAScript Harmony. Features under discussion for Harmony at the time included

The intent of these features was 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.[19][20] These fixes and others, and support for JSON encoding/decoding, have been folded into the ECMAScript, 5th Edition specification.[21]

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,"[22] and that stakeholders who opposed the changes were being "hidden from view".[23] 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.[24] 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.[25]

5th Edition

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.[26][27] 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.[28] On December 3, 2009, ECMA-262 5th edition was published.[29]

6th Edition - ECMAScript 2015

The 6th edition, officially known as ECMAScript 2015, was finalized in June 2015.[12][30] This update 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, typed arrays, collections (maps, sets and weak maps), promises, number and math enhancements, reflection, and proxies (metaprogramming for virtual objects and wrappers).[31][32] The complete list is extensive.[33]

Browser support for ES2015 is still incomplete.[34] However, ES2015 code can be transpiled into ES5 code, which has more consistent support across browsers.[35] Transpiling adds an extra step to build processes whereas polyfills allow adding extra functionalities by including another JavaScript file.

7th Edition - ECMAScript 2016

The 7th edition, officially known as ECMAScript 2016, was finalized in June 2016.[13] New features include the exponentiation operator (**), Array.prototype.includes (not to be confused with ClassList.contains).

8th Edition - ECMAScript 2017

The 8th edition, officially known as ECMAScript 2017, was finalized in June 2017.[10] Includes await/async, which works using generators and promises.


ES.Next is a dynamic name that refers to whatever the next version is at time of writing. ES.Next features are more correctly called proposals, because, by definition, the specification has not been finalized yet.


The ECMAScript language includes structured, dynamic, functional, and prototype-based features.[36]



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] 2017[37][d 2]
V8 Google Chrome, Node.js, Opera, others 2017[37][d 3]
JavaScriptCore (Nitro) WebKit, Safari, Qt 5 2017[38]
Chakra Microsoft Edge 5.1 and features from 2015,[d 4] 2016 and 2017[37]
JerryScript Resource constrained IoT devices, Pebble 5.1[39]
JScript 9.0 Internet Explorer, the Trident layout engine 5.1[40]
Nashorn Java 9 6[41]
Nashorn Java 5.1[42]
Rhino Java Platform, Standard Edition 3
Carakan (deprecated) Opera 12 5.1[43][d 5]
KJS KHTML 5.1 and features from 2015[]
Ejscript Appweb Web Server, Samba 4 2015[44]
JScript .NET Microsoft .NET Framework 3[d 6]
ActionScript Adobe Flash, Adobe Flex, Adobe AIR 4[45]
ExtendScript Adobe Creative Suite products: InDesign, Illustrator, Photoshop,
Bridge, After Effects, Premiere Pro
InScript iCab 3
Max/MSP engine Max 3
QtScript (deprecated) KDE SC 4 3
Caja 5[47]
Jsi Javascript Interpreter Shell - Embeddable javascript interpreter[48] 5.1 and features from 6[49]
  1. ^ Adobe Acrobat X uses the SpiderMonkey 1.8 engine: JavaScript for Acrobat
  2. ^ According to the widely used compatibility table, Firefox supports the vast majority, but not all, of the features introduced in ECMAScript 2015. See Tracking bug for ECMAScript 6 in SpiderMonkey for missing features.
  3. ^ According to the widely used compatibility table, Chrome supports the vast majority, but not all, of the features introduced in ECMAScript 2015.
  4. ^ Microsoft states that Edge "supports most ES2015 features," supporting 81% of the specification as of May 2015 and 96% as of April 2017.[1][2]
  5. ^ Opera's implementation includes some JavaScript and JScript extensions: ECMAScript support in Opera Presto 2.3
  6. ^ 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.

Version correspondence

Items on the same line are approximately the same language.[50][51]

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)[52]

Conformance tests

In 2010, Ecma International started developing a standards test for Ecma 262 ECMAScript.[53] 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.

See also


  1. ^ Stefanov, Stoyan (2010). JavaScript Patterns. O'Reilly Media, Inc. p. 5. ISBN 9781449396947. Retrieved . The core JavaScript programming language [...] is based on the ECMAScript standard, or ES for short. 
  2. ^ "TC39 - ECMAScript® (formerly TC39-TG1)". Ecma International. Retrieved 2015. 
  3. ^ "A Short History of JavaScript". W3C. Retrieved 2017. 
  4. ^ Krill, Paul (2008-06-23). "JavaScript creator ponders past, future". InfoWorld. Retrieved . 
  5. ^ "Netscape and Sun Announce JavaScript, the Open, Cross-platform Object Scripting Language for Enterprise Networks and the Internet". Netscape. December 4, 1995. Archived from the original on 2007-09-16. Retrieved . 
  6. ^ "Brendan's Roadmap Updates: Popularity". Archived from the original on 17 May 2008. 
  7. ^ "Industry Leaders to Advance Standardization of Netscape's JavaScript at Standards Body Meeting". Netscape. November 15, 1996. Archived from the original on 1998-12-03. Retrieved . 
  8. ^ "Will there be a suggested file suffix for es4?". 2006-10-03. Retrieved . 
  9. ^ "JScript VS JavaScript". 2015-11-25. 
  10. ^ a b c "ECMAScript 2017 Language Specification". Ecma International. June 2017. 
  11. ^ "Changes to JavaScript, Part 1: EcmaScript 5". YouTube. 2009-05-18. Retrieved . 
  12. ^ a b c "ECMAScript 2015 Language Specification". Ecma International. June 2015. 
  13. ^ a b c "ECMAScript 2016 Language Specification". Ecma International. June 2016. 
  14. ^ "strawman:strawman [ES Wiki]". 2013-09-18. Retrieved . 
  15. ^ "tc39/ecma262". TC39. GitHub. Retrieved 2015. 
  16. ^ 2015-03-24 Meeting Notes. ESDiscuss. Also see Ecma withdrawn Standards. ECMA.
  17. ^ "ES4 overview paper released". Retrieved . 
  18. ^ "Proposed ECMAScript 4th Edition - Language Overview" (PDF). 23 October 2007. Archived from the original (PDF) on 13 July 2010. 
  19. ^ John Resig. "John Resig - Bug Fixes in JavaScript 2". Retrieved . 
  20. ^ "Compatibility Between ES3 and Proposed ES4" (PDF). Retrieved . 
  21. ^
  22. ^ "ECMAScript 3 and Beyond - IEBlog - Site Home - MSDN Blogs". 2007-10-30. Retrieved . 
  23. ^ "What I think about ES4. - Albatross! - Site Home - MSDN Blogs". 2007-10-31. Retrieved . 
  24. ^ "Open letter to Chris Wilson". Brendan Eich. 2007-10-31. Retrieved . 
  25. ^ "JavaScript 2 and the Open Web". 2007-11-20. Retrieved . 
  26. ^ "ECMAScript Harmony". Retrieved . 
  27. ^ "A Major Milestone in JavaScript Standardization - JScript Blog - Site Home - MSDN Blogs". 2009-04-09. Retrieved . 
  28. ^ "Ecma International finalises major revision of ECMAScript". Ecma International. 2009-04-09. Retrieved . 
  29. ^ "Ecma latest news". Retrieved . 
  30. ^
  31. ^
  32. ^
  33. ^
  34. ^ "ECMAScript 6 compatibility table". 
  35. ^
  36. ^ "About". ECMAScript. Archived from the original on 2012-08-02. Retrieved . 
  37. ^ a b c "ECMAScript 2016+ compatibility table". 
  38. ^ "Safari 10.1". Apple Developer. 24 January 2017. Support for ECMAScript 2016 and ECMAScript 2017 is available in Safari for macOS and iOS. 
  39. ^ "Samsung/jerryscript". GitHub. Retrieved . 
  40. ^ "JavaScript Language Reference". Microsoft Docs. Retrieved . 
  41. ^ "JEP 292: Implement Selected ECMAScript 6 Features in Nashorn". Retrieved . 
  42. ^ "Nashorn extensions". OpenJDK Wiki. Retrieved . 
  43. ^ "Full ECMAScript 5.1 support in Opera 11.51+". Opera Desktop Team blog. 2011-09-13. Archived from the original on 2011-11-24. 
  44. ^ "Ejscript Overview". Embedthis Software. Retrieved . 
  45. ^ Darrick Brown (May 25, 2006). "AS3 language 101 for C/C++ coders". Adobe Blogs: The Kiwi Project. 
  46. ^
  47. ^ "Caja Introduction". Google Developers. February 28, 2012. 
  48. ^ "Jsish". November 23, 2017. 
  49. ^ "Jsish Background". November 23, 2017. 
  50. ^ tedster (March 12, 2002). "JavaScript - JScript - ECMAScript version history". Retrieved . 
  51. ^ "Version Information (JScript)". Archived from the original on 2009-12-17. Retrieved . 
  52. ^ Andrew Clinick (July 14, 2000). "Introducing JScript .NET". Retrieved . 
  53. ^ "ECMAScript Language - test262". Archived from the original on 2011-05-14. Retrieved . 

External links

ISO Standard
Ecma Standards

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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