ECMAScript

ECMA-262, or the ECMAScript Language Specification, defines the ECMAScript Language, or just ECMAScript.{{cite web |last=Guo |first=Shu-yu |date=2022-02-14 |title=ECMAScriptÂŽ 2022 Language Specification |url=https://tc39.es/ecma262/ |url-status=live |archive-url=https://web.archive.org/web/20200508053013/https://tc39.es/ecma262/ |archive-date=2020-05-08 |website=tc39.es |accessdate=2022-02-14}} ECMA-262 specifies only language syntax and the semantics of the core application programming interface (API), such as {{mono|Array}}, {{mono|Function}}, and {{mono|globalThis}}, while valid implementations of JavaScript add their own functionality such as input/output and file system handling.

The ECMAScript specification is a standardized specification of a scripting language developed by Brendan Eich of Netscape; initially named Mocha, then LiveScript, and finally JavaScript.{{cite web |last=Krill |first=Paul |date=2008-06-23 |title=JavaScript creator ponders past, future |url=http://www.infoworld.com/article/2653798/application-development/javascript-creator-ponders-past--future.html |url-status=live |archive-url=https://web.archive.org/web/20140920141040/http://www.infoworld.com/article/2653798/application-development/javascript-creator-ponders-past--future.html |archive-date=2014-09-20 |access-date=2013-10-31 |website=infoworld.com |publisher=InfoWorld}} In December 1995, Sun Microsystems and Netscape announced JavaScript in a press release.{{cite web |date=1995-12-04 |title=Netscape and Sun announce JavaScript, the Open, Cross-platform Object Scripting Language for Enterprise Networks and the Internet |url=http://wp.netscape.com/newsref/pr/newsrelease67.html |url-status=dead |archive-url=https://web.archive.org/web/20020606002913/http://wp.netscape.com/newsref/pr/newsrelease67.html |archive-date=2002-06-06 |access-date=2019-11-04 |website=Netscape.com |publisher=Netscape}} In November 1996, Netscape announced a meeting of the Ecma International standards organization to advance the standardization of JavaScript.{{cite web |last=Press Release |date=November 15, 1996 |title=Industry Leaders to Advance Standardization of Netscape's JavaScript at Standards Body Meeting |url=http://cgi.netscape.com/newsref/pr/newsrelease289.html |url-status=dead |archive-url=https://web.archive.org/web/19981203070212/http://cgi.netscape.com/newsref/pr/newsrelease289.html |archive-date=1998-12-03 |access-date=2013-10-31 |website=Netscape.com |publisher=Netscape}} 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."{{cite web |last=Eich |first=Brendan |date=2006-10-03 |title=Will there be a suggested file suffix for es4? |url=https://mail.mozilla.org/pipermail/es-discuss/2006-October/000133.html |url-status=live |archive-url=https://web.archive.org/web/20200621202321/https://mail.mozilla.org/pipermail/es-discuss/2006-October/000133.html |archive-date=2020-06-21 |access-date=2021-05-05 |website=mozilla.org |publisher=Mail.mozilla.org}} ECMAScript has been formalized through operational semantics by work at Stanford University and the Department of Computing, Imperial College London for security analysis and standardization.{{cite web |last1=Maffeis |first1=Sergio |last2=Mitchell |first2=John C. |last3=Taly |first3=Ankur |date=2020-01-03 |title=An Operational Semantics for JavaScript |url=http://theory.stanford.edu/people/jcm/papers/aplas08-camera-ready.pdf |url-status=live |archive-url=https://web.archive.org/web/20200103204704/http://theory.stanford.edu/people/jcm/papers/aplas08-camera-ready.pdf |archive-date=2020-01-03 |access-date=2020-01-03 |website=stanford.edu |publisher=Association for Computing Machinery}}

"ECMA" stood for "European Computer Manufacturers Association" until 1994.

{{Main|ECMAScript version history}}

Ecma's Technical Committee 39 (TC39) is responsible for the maintenance of ECMAScript.{{Citation |title=TC39 |work=Technical Committees |url=https://ecma-international.org/technical-committees/tc39 |access-date=2024-08-11 |publisher=Ecma International |language=en-US}} New proposals to the language go through a staged process, with each stage representing the completeness of the proposal's specification. Consensus must be reached within the committee to advance a proposal to the next stage. Proposals that reach stage 4, the final stage, will be included into the next version of the standard.{{Citation |title=The TC39 Process |work=TC39 |url=https://tc39.es/process-document |access-date=2024-08-11 |publisher=Ecma International}} Since the release of version 6 in June 2015, new major versions have been finalized and published every June.{{Citation |title=ECMAScript, TC39, and the History of JavaScript |work=ui.dev |url=https://ui.dev/ecmascript |access-date=2024-08-11}}

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{{main|ECMAScript syntax|JavaScript#Features}}

The ECMAScript language includes structured, dynamic, functional, and prototype-based features.{{cite web |url=http://www.ecmascript.org/about.php |title=About |publisher=ECMAScript |access-date=2009-12-17 |url-status=dead |archive-url=https://archive.today/20120802115457/http://www.ecmascript.org/about.php |archive-date=2012-08-02 }}

ECMAScript JavaScript supports C-style structured programming. Previously, JavaScript only supported function scoping using the keyword var, but ECMAScript 2015 added the keywords let and const, allowing JavaScript to support both block scoping and function scoping. JavaScript supports automatic semicolon insertion, meaning that semicolons that normally terminate a statement in C may be omitted in JavaScript.{{cite book|title=JavaScript: The Definitive Guide|first=David|last=Flanagan|edition=5th|date=17 August 2006|publisher=O'Reilly|isbn=978-0-596-10199-2|page=16|url=https://archive.org/details/javascriptdefini0000flan|url-access=registration}}

Like C-style languages, control flow is done with the {{Code|code=while}}, {{Code|code=for}}, {{Code|code=do}} / {{Code|code=while}}, {{Code|code=if}} / {{Code|code=else}}, and {{Code|code=switch}} statements. Functions are weakly typed and may accept and return any type. Arguments not provided default to {{Code|code=undefined}}.

ECMAScript is weakly typed. This means that certain types are assigned implicitly based on the operation being performed. However, there are several quirks in JavaScript's implementation of the conversion of a variable from one type to another. These quirks have been the subject of a talk entitled Wat.{{cite conference |last1=Bernhardt |first1=Gary |title=Wat |url=https://www.destroyallsoftware.com/talks/wat |website=Destroy All Software |conference=CodeMash 2012 |access-date=2021-08-18 |archive-date=2019-10-28 |archive-url=https://web.archive.org/web/20191028204723/https://www.destroyallsoftware.com/talks/wat |url-status=live }}{{cite magazine |last1=Gilbertson |first1=Scott |title=Jokes for Nerds: Wat Moments in Programming |url=https://www.wired.com/2012/01/jokes-for-nerds-wat-moments-in-programming/ |access-date=22 August 2021 |magazine=Wired |date=26 January 2012 |archive-date=23 August 2020 |archive-url=https://web.archive.org/web/20200823123837/https://www.wired.com/2012/01/jokes-for-nerds-wat-moments-in-programming/ |url-status=live }}

ECMAScript is dynamically typed. Thus, a type is associated with a value rather than an expression. ECMAScript supports various ways to test the type of objects, including duck typing.{{cite web|url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures|title=JavaScript data types and data structures – JavaScript {{pipe}} MDN|date=2017-02-16|website=Developer.mozilla.org|access-date=2017-02-24|archive-date=2017-03-14|archive-url=https://web.archive.org/web/20170314230542/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures|url-status=live}}

{{Main|JavaScript#transpilers}}

Since ES 2015, transpiling JavaScript has become very common. Transpilation is a source-to-source compilation in which newer versions of JavaScript are used, and a transpiler rewrites the source code so that it is supported by older browsers. Usually, transpilers transpile down to ES3 to maintain compatibility with all versions of browsers. The settings to transpile to a specific version can be configured according to need. Transpiling adds an extra step to the build process and is sometimes done to avoid needing polyfills. Polyfills create new features for older environments that lack them. Polyfills do this at runtime in the interpreter, such as the user's browser or on the server. Instead, transpiling rewrites the ECMA code itself during the build phase of development before it reaches the interpreter.

In 2010, Ecma International started developing a standards test for Ecma 262 ECMAScript.{{cite web |url=http://test262.ecmascript.org/ |title=ECMAScript Language – test262 |publisher=Test262.ecmascript.org |access-date=2013-10-31 |url-status=dead |archive-url=https://web.archive.org/web/20110514205704/http://test262.ecmascript.org/ |archive-date=2011-05-14 }}

Test262 is an ECMAScript conformance test suite that can be used to check how closely a JavaScript implementation follows the ECMAScript Specification. The test suite contains thousands of individual tests, each of which tests some specific requirement(s) of the ECMAScript specification. The development of Test262 is a project of the Ecma Technical Committee 39 (TC39). The testing framework and the individual tests are contributed to Ecma by member organizations of TC39.

Important contributions were made by Google (Sputnik test suite) and Microsoft, who both contributed thousands of tests.

The Test262 test suite consisted of {{val|38014}} tests {{as of|2020|01|lc=y}}.{{cite web | title=tc39/test262 | website=GitHub | date=January 24, 2020 | url=https://github.com/tc39/test262 | access-date=January 29, 2020 | archive-date=October 1, 2019 | archive-url=https://web.archive.org/web/20191001032806/https://github.com/tc39/test262 | url-status=live }} 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.

• ECMAScript for XML (E4X)
• List of ECMAScript engines

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Category:Ecma standards

Category:Object-based programming languages

Category:Programming languages with an ISO standard

Category:Scripting languages

Category:Source-to-source compilers