|Paradigm||Multi-paradigm: prototype-based, functional, imperative|
|Designed by||Brendan Eich, Ecma International|
|Typing discipline||weak, dynamic|
|Self, HyperTalk, AWK, C, Perl, Python, Java, Scheme|
|Internet media type||
|Initial release||June 1997|
(June 2017 )
|Type of format||Scripting language|
There are eight editions of ECMA-262 published. Work on version 8 of the standard was finalized in June 2017.
|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.||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||The sixth edition, initially known as ECMAScript 6 (ES6) and later renamed to ECMAScript 2015 (ES2015) 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||ECMAScript 2016 (ES2016), the seventh edition, 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 (
|8||June 2017||ECMAScript 2017 (ES2017), the eighth edition, includes features for concurrency and atomics, syntactic integration with promises (async/await).||Brian Terlson|
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.
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. An overview of the language was released by the working group on October 23, 2007.
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
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. These fixes and others, and support for JSON encoding/decoding, have been folded into the ECMAScript, 5th Edition specification.
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. 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. On December 3, 2009, ECMA-262 5th edition was published.
The 6th edition, officially known as ECMAScript 2015, was finalized in June 2015. 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, 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). The complete list is extensive.
The 7th edition, officially known as ECMAScript 2016, was finalized in June 2016. New features include the exponentiation operator (**), Array.prototype.includes (not to be confused with ClassList.contains).
The 9th edition, officially known as ECMAScript 2018, is in draft status as of June 2018 but the features that will be included have been finalized. These would be rest/spread properties, asynchronous iteration, Promise.prototype.finally and additions to RegExp.
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.
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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.
ECMAScript specifications through ES7 are well-supported in major web browsers. The table below shows the conformance rate for current versions of software with respect to the most recent editions of ECMAScript.
|Scripting engine||Reference application(s)||Conformance|
|Chrome V8||Google Chrome, Opera||100%||98%||100%||93%|
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