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{{Short description|High-level programming language}}
{{Distinguish|Java (programming language)|Javanese script|ECMAScript}}
{{pp-semi-indef|small=yes}}
{{Use dmy dates|date=March 2024}}
{{Infobox programming language
| name = JavaScript
| logo = <!-- Do not add
| logo alt =
| screenshot = JavaScript code.png
| screenshot caption = Screenshot of JavaScript source code
|
| memory management = [[Garbage collection (computer science)|Garbage collected]]
| family = [[ECMAScript]]
| designers = [[Brendan Eich]] of [[Netscape]] first; then others contributed to [[ECMAScript]] standard
| typing = [[Dynamic typing|Dynamic]], [[Strong and weak typing|weak]], [[Duck typing|duck]]
| scope = [[Scope (computer science)|lexical]]
| released = {{Start date and age|1995|12|04|df=y}}<ref name="press_release">{{Cite press release |url=https://wp.netscape.com/newsref/pr/newsrelease67.html |archive-url=https://web.archive.org/web/20070916144913/https://wp.netscape.com/newsref/pr/newsrelease67.html |archive-date=2007-09-16 |title=Netscape and Sun announce JavaScript, the Open, Cross-platform Object Scripting Language for Enterprise Networks and the Internet |date=December 4, 1995}}</ref>
| latest release version = {{wikidata|property|edit|reference|P548=Q2804309|P348}}
| latest release date = {{start date and age|{{wikidata|qualifier|single|P548=Q2804309|P348|P577}}}}
| latest preview version = {{wikidata|property|edit|reference|P548=Q51930650|P348}}
| latest preview date = {{start date and age|{{wikidata|qualifier|single|P548=Q51930650|P348|P577}}}}
| license =
| file extensions = <code>.js</code> • <code>.mjs</code> • <code>.cjs</code><ref name="node.js ECMAScript Modules Specification">{{cite web|url=https://github.com/nodejs/node-eps/blob/master/002-es-modules.md|title=nodejs/node-eps|website=GitHub|access-date=2018-07-05|archive-date=2020-08-29|archive-url=https://web.archive.org/web/20200829024713/https://github.com/nodejs/node-eps/blob/master/002-es-modules.md|url-status=live}}</ref>
| file format =
| website = {{URL|https://ecma-international.org/publications-and-standards/standards/ecma-262/}}
| implementations = [[V8 (JavaScript engine)|V8]], [[JavaScriptCore]], [[SpiderMonkey]];<br/>[[Chakra (JavaScript engine)|Chakra]] (deprecated)
| influenced by = [[Java (programming language)|Java]],<ref name="looklikejava">{{cite book |last1=Seibel |first1=Peter |date=September 16, 2009 |title=Coders at Work: Reflections on the Craft of Programming |publisher=Apress |isbn=978-1-4302-1948-4 |quote=Eich: The immediate concern at Netscape was it must look like Java. |url=https://books.google.com/books?id=nneBa6-mWfgC&q=The+immediate+concern+at+Netscape+was+it+must+look+like+Java.&pg=PA141 |access-date=December 25, 2018 |url-status=live |archive-url=https://web.archive.org/web/20201224233514/https://books.google.com/books?id=nneBa6-mWfgC&q=The+immediate+concern+at+Netscape+was+it+must+look+like+Java.&pg=PA141 |archive-date=December 24, 2020}}</ref><ref name="origin"/> [[Scheme (programming language)|Scheme]],<ref name="origin"/> [[Self (programming language)|Self]],<ref>{{cite web |url=https://brendaneich.com/2008/04/popularity/ |title = Popularity – Brendan Eich}}</ref> [[AWK]],<ref>{{cite web |title=Brendan Eich: An Introduction to JavaScript, JSConf 2010 |website=[[YouTube]] |date=20 January 2013 |quote=Eich: "function", eight letters, I was influenced by AWK. |url=https://www.youtube.com/watch?v=1EyRscXrehw |access-date=November 25, 2019 |page=22m |url-status=live |archive-url=https://web.archive.org/web/20200829024704/https://www.youtube.com/watch?v=1EyRscXrehw |archive-date=August 29, 2020}}</ref> [[HyperTalk]]<ref>{{cite book |last1=Eich |first1=Brendan |author1-link=Brendan Eich |chapter=Foreword |editor1-last=Goodman |editor1-first=Danny |editor1-link=Danny Goodman |year=1998 |title=JavaScript Bible |edition=3rd |publisher=[[John Wiley & Sons]] |isbn=0-7645-3188-3 |lccn=97078208 |oclc=38888873 |ol=712205M |url-access=registration |url=https://archive.org/details/javascriptbible000good}}</ref>
| influenced = [[ActionScript]], [[ArkTS]], [[AssemblyScript]], [[CoffeeScript]], [[Dart (programming language)|Dart]], [[Haxe]], [[JS++]], [[Opa (programming language)|Opa]], [[TypeScript]]
| wikibooks = JavaScript
}}
'''JavaScript''' ('''JS'''){{efn|{{IPAc-en|ˈ|dʒ|ɑː|v|ə|s|k|r|ɪ|p|t
[[Web browser]]s have a dedicated [[JavaScript engine]] that executes the client [[Source code|code]]. These engines are also utilized in some [[Server (computing)|servers]] and a variety of [[Application software|apps]]. The most popular [[runtime system]] for non-browser usage is [[Node.js]]{{cn|date=August 2025}}.
JavaScript is a [[High-level programming language|high-level]], often [[Just-in-time compilation|just-in-
The ECMAScript standard does not include any [[input/output]] (I/O), such as [[computer network|networking]], [[data storage|storage]], or [[computer graphics|graphics]] facilities. In practice, the web browser or other
Although [[Java (programming language)|Java]] and JavaScript are similar in name and [[Syntax (programming languages)|syntax]], the two languages are distinct and differ greatly in design.
== History ==
=== Creation at Netscape ===
The first popular [[web browser]] with a [[graphical user interface]], [[Mosaic (web browser)|Mosaic]], was released in 1993. The lead developers of Mosaic then founded the [[Netscape]] corporation, which released a more polished browser, [[Netscape Navigator]], in 1994. This quickly became the most-used.<ref>{{cite web|url=https://www.mwdwebsites.com/nj-web-design-web-browsers.html|title=The Evolution of the Web Browsers|last=Enzer|first=Larry|date=August 31, 2018|website=Monmouth Web Developers|access-date=August 31, 2018|archive-date=August 31, 2018|archive-url=https://web.archive.org/web/20180831174847/https://www.mwdwebsites.com/nj-web-design-web-browsers.html|url-status=dead}}</ref>
During these formative years of the Web, [[web page]]s could only be static, lacking the capability for dynamic behavior after the page was loaded in the browser. There was a desire in the flourishing web development scene to remove this limitation, so in 1995, Netscape decided to add a [[programming language]] to Navigator. They pursued two routes to achieve this: collaborating with [[Sun Microsystems]] to embed the [[Java (programming language)|Java]] language, while also hiring [[Brendan Eich]] to embed the [[Scheme (programming language)|Scheme]] language.<ref name="origin">{{cite web|url=https://exploringjs.com/es5/ch04.html|title=Chapter 4. How JavaScript Was Created|website=speakingjs.com|access-date=2017-11-21|archive-date=2020-02-27|archive-url=https://web.archive.org/web/20200227184037/https://speakingjs.com/es5/ch04.html|url-status=live}}</ref>
The goal was a "language for the masses",<ref name="EichVideo" /> "to help nonprogrammers create dynamic, interactive [[website|Web sites]]".<ref>"Netscape Communications Corp.", Browser enhancements. Encyclopædia Britannica 2006 Ultimate Reference Suite DVD</ref> Netscape management soon decided that the best option was for Eich to devise a new language, with syntax similar to Java and less like Scheme or other extant [[scripting language]]s.<ref name="looklikejava" /><ref name="origin" /> Although the new language and its [[Interpreter (computing)|interpreter]] implementation were called LiveScript when first shipped as part of a Navigator [[beta software|beta]] in September 1995, the name was changed to JavaScript for the official release in December.<ref name="origin" /><ref name="press_release" /><ref name="techvision">{{cite web | archive-url=https://web.archive.org/web/20080208124612/https://wp.netscape.com/comprod/columns/techvision/innovators_be.html | archive-date=February 8, 2008 | title=TechVision: Innovators of the Net: Brendan Eich and JavaScript | url=https://wp.netscape.com/comprod/columns/techvision/innovators_be.html }}</ref><ref name="wired2024">{{cite magazine |last1=Han |first1=Sheon |title=JavaScript Runs the World—Maybe Even Literally |url=https://www.wired.com/story/javascript-runs-the-world-maybe-literally/ |magazine=Wired |date=4 March 2024 |access-date=21 August 2024}}</ref>
The choice of the ''JavaScript'' name has caused confusion, implying that it is directly related to Java. At the time, the [[Dot-com bubble|dot-com boom]] had begun and Java was a popular new language, so Eich considered the JavaScript name a marketing ploy by Netscape.<ref name="EichVideo">{{Citation|last=Fin JS|title=Brendan Eich – CEO of Brave|date=June 17, 2016|url=https://www.youtube.com/watch?v=XOmhtfTrRxc |website=YouTube |access-date=February 7, 2018 }}</ref>
=== Adoption by Microsoft ===
[[Microsoft]] debuted [[Internet Explorer]] in 1995, leading to a [[browser war]] with Netscape. On the JavaScript front, Microsoft created its own [[Interpreter (computing)|interpreter]] called [[JScript]].<ref name="sjsch5">{{cite web |title=Chapter 5. Standardization: ECMAScript |url=https://speakingjs.com/es5/ch05.html |website=speakingjs.com |access-date=1 November 2021 |archive-date=1 November 2021 |archive-url=https://web.archive.org/web/20211101184346/http://speakingjs.com/es5/ch05.html |url-status=dead }}</ref>
Microsoft first released JScript in 1996, alongside initial support for [[CSS]] and extensions to [[HTML]]. Each of these [[implementation]]s was noticeably different from their counterparts in [[Netscape Navigator]].<ref name="O'Reilly-2001">{{cite web |url=https://archive.oreilly.com/pub/a/javascript/2001/04/06/js_history.html |title=JavaScript, How Did We Get Here? |last=Champeon |first=Steve |date=April 6, 2001 |website=oreilly.com |access-date=July 16, 2016 |archive-url=https://web.archive.org/web/20160719020828/https://archive.oreilly.com/pub/a/javascript/2001/04/06/js_history.html |archive-date=July 19, 2016 |url-status=dead}}</ref><ref>{{cite web |url=https://news.microsoft.com/1996/05/29/microsoft-internet-explorer-3-0-beta-now-available/ |title=Microsoft Internet Explorer 3.0 Beta Now Available |publisher=Microsoft |date=May 29, 1996 |website=microsoft.com |access-date=July 16, 2016 |archive-date=November 24, 2020 |archive-url=https://web.archive.org/web/20201124154053/https://news.microsoft.com/1996/05/29/microsoft-internet-explorer-3-0-beta-now-available/ |url-status=live }}</ref> These differences made it difficult for developers to make their websites work well in both browsers, leading to widespread use of "best viewed in Netscape" and "best viewed in Internet Explorer" logos for several years.<ref name="O'Reilly-2001" /><ref>{{cite web |url=https://www.technologizer.com/2010/09/16/the-unwelcome-return-of-best-viewed-with-internet-explorer/ |title=The Unwelcome Return of "Best Viewed with Internet Explorer" |last=McCracken |first=Harry |date=September 16, 2010 |website=technologizer.com |access-date=July 16, 2016 |archive-date=June 23, 2018 |archive-url=https://web.archive.org/web/20180623192402/https://www.technologizer.com/2010/09/16/the-unwelcome-return-of-best-viewed-with-internet-explorer/ |url-status=live }}</ref>
=== The rise of JScript ===
{{Quote box|[[Brendan Eich]] later said of this period: "It's still kind of a [[sidekick]] language. It's considered slow or annoying. People do [[Pop-up ad|pop-ups]] or those scrolling messages in the old [[status bar]] at the bottom of your old [[web browser|browser]]."<ref name="EichVideo" />|width=30%}}
In November 1996, [[Netscape]] submitted JavaScript to [[Ecma International]], as the starting point for a standard specification that all browser vendors could conform to. This led to the official release of the first [[ECMAScript]] language specification in June 1997.
The standards process continued for a few years, with the release of ECMAScript 2 in June 1998 and ECMAScript 3 in December 1999. Work on ECMAScript 4 began in 2000.<ref name="sjsch5" />
Microsoft initially participated in the standards process and implemented some proposals in its JScript language, but eventually it stopped collaborating on
=== Growth and standardization ===
{{Plain image with caption|Logo of TC39.svg|Logo of [[Ecma International]] Technical Committee 39 who is responsible for maintaining the standard|150px}}
During the period of [[Internet Explorer]] dominance in the early 2000s, client-side scripting was stagnant. This started to change in 2004, when the successor of Netscape, [[Mozilla]], released the [[Firefox]] browser. Firefox was well received by many, taking significant market share from Internet Explorer.<ref>{{cite news |url=https://news.bbc.co.uk/2/hi/business/4508897.stm |title=The assault on software giant Microsoft |last=Weber |first=Tim |date=May 9, 2005 |work=[[BBC News]] |archive-url=https://web.archive.org/web/20170925233936/https://news.bbc.co.uk/2/hi/business/4508897.stm |archive-date=September 25, 2017}}</ref>
In 2005, Mozilla joined ECMA International, and work started on the [[ECMAScript for XML]] (E4X) standard. This led to Mozilla working jointly with [[Macromedia]] (later acquired by [[Adobe Systems]]), who were implementing E4X in their ActionScript 3 language, which was based on an ECMAScript 4 draft. The goal became standardizing ActionScript 3 as the new ECMAScript 4. To this end, Adobe Systems released the [[Tamarin (software)|Tamarin]] implementation as an [[Open-source model|open source]] project. However, Tamarin and ActionScript 3 were too different from established client-side scripting, and without cooperation from
Meanwhile, very important developments were occurring in open-source communities not affiliated with ECMA work. In 2005, [[Jesse James Garrett]] released a white paper in which he coined the term [[Ajax (programming)|Ajax]] and described a set of technologies, of which JavaScript was the backbone, to create [[web application]]s where data can be loaded in the background, avoiding the need for full page reloads. This sparked a renaissance period of JavaScript, spearheaded by open-source libraries and the communities that formed around them. Many new libraries were created, including [[jQuery]], [[Prototype JavaScript Framework|Prototype]], [[Dojo Toolkit]], and [[MooTools]].
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In July 2008, these disparate parties came together for a conference in [[Oslo]]. This led to the eventual agreement in early 2009 to combine all relevant work and drive the language forward. The result was the ECMAScript 5 standard, released in December 2009.
=== Reaching maturity ===
Ambitious work on the language continued for several years, culminating in an extensive collection of additions and refinements being formalized with the publication of [[ECMAScript
The creation of [[Node.js]] in 2009 by [[Ryan Dahl]] sparked a significant increase in the usage of JavaScript outside of web browsers. Node combines the [[V8 (JavaScript engine)|V8]] engine, an [[event loop]], and [[Input/output|I/O]] [[Application programming interface|APIs]], thereby providing a stand-alone JavaScript runtime system.<ref>[https://books.google.com/books?id=ZH6bpbcrlvYC&q=nodejs Professional Node.js: Building JavaScript Based Scalable Software] {{Webarchive|url=https://web.archive.org/web/20170324021220/https://books.google.com/books?id=ZH6bpbcrlvYC&printsec=frontcover&dq=nodejs&hl=en&sa=X#v=onepage&q=nodejs&f=false |date=2017-03-24 }}, John Wiley & Sons, 01-Oct-2012</ref><ref name="b3">[https://books.google.com/books?id=KGt-FxUEj48C&dq=nodejs&pg=PT24 Sams Teach Yourself Node.js in 24 Hours] {{Webarchive|url=https://web.archive.org/web/20170323192039/https://books.google.com/books?id=KGt-FxUEj48C&pg=PT24&dq=nodejs&hl=en&sa=X#v=onepage&q=nodejs&f=false |date=2017-03-23 }}, Sams Publishing, 05-Sep-2012</ref> As of 2018, Node had been used by millions of developers,<ref>{{cite web |last1=Lawton |first1=George |title=The secret history behind the success of npm and Node |url=https://www.theserverside.com/blog/Coffee-Talk-Java-News-Stories-and-Opinions/The-secret-history-behind-the-success-of-npm-and-Node |website=TheServerSide |access-date=2 August 2021 |date=19 July 2018 |archive-date=2 August 2021 |archive-url=https://web.archive.org/web/20210802165613/https://www.theserverside.com/blog/Coffee-Talk-Java-News-Stories-and-Opinions/The-secret-history-behind-the-success-of-npm-and-Node |url-status=live }}</ref> and [[npm (software)|npm]] had the most modules of any [[package manager]] in the world.<ref>{{cite web |last1=Brown |first1=Paul |title=State of the Union: npm |url=https://www.linux.com/news/state-union-npm/ |website=Linux.com |access-date=2 August 2021 |date=13 January 2017 |archive-date=2 August 2021 |archive-url=https://web.archive.org/web/20210802165614/https://www.linux.com/news/state-union-npm/ |url-status=live }}</ref>
The ECMAScript draft specification is currently
The current JavaScript ecosystem has many [[List of JavaScript libraries|libraries]] and [[web framework|frameworks]], established programming practices, and substantial usage of JavaScript outside of web browsers.<ref name="wired2024" /> Plus, with the rise of [[single-page application]]s and other JavaScript-heavy websites, several [[source-to-source compiler|transpilers]] have been created to aid the development process.<ref name="transpilers" />
== Trademark ==
"JavaScript" is a [[trademark]] of [[Oracle Corporation]] in the United States.<ref>{{cite web |date=1997-05-06 |title=U.S. Trademark Serial No. 75026640 |url=https://tsdr.uspto.gov/#caseNumber=75026640&caseType=SERIAL_NO&searchType=statusSearch |url-status=live |archive-url=https://web.archive.org/web/20210713022850/https://tsdr.uspto.gov/#caseNumber=75026640&caseType=SERIAL_NO&searchType=statusSearch |archive-date=2021-07-13 |access-date=2021-05-08 |website=uspto.gov |publisher=[[United States Patent and Trademark Office]]}}</ref><ref>{{cite web |title=Legal Notices |url=https://www.oracle.com/legal/trademarks.html |url-status=live |archive-url=https://web.archive.org/web/20210605142505/https://www.oracle.com/legal/trademarks.html |archive-date=2021-06-05 |access-date=2021-05-08 |website=oracle.com |publisher=[[Oracle Corporation]]}}</ref> The trademark was originally issued to [[Sun Microsystems]] on 6 May 1997, and was transferred to Oracle when they acquired Sun in 2009.<ref>{{Cite news |title=Oracle to buy Sun in $7.4-bn deal | newspaper=The Economic Times |url=https://economictimes.indiatimes.com/tech/software/oracle-to-buy-sun-in-7-4-bn-deal/articleshow/4427747.cms | date = 21 April 2009}}</ref><ref>{{Cite news |title=Oracle urged again to give up JavaScript trademark |work=The Register |url=https://www.theregister.com/2024/09/17/oracle_urged_to_surrender_javascript_trademark/ |date=17 September 2024 |last1=Claburn |first1=Thomas |access-date=2 February 2025}}</ref>
A letter was circulated in September 2024, spearheaded by [[Ryan Dahl]], calling on Oracle to free the JavaScript trademark.<ref>{{Cite news|last=Krill|first=Paul|date=September 20, 2024|title=JavaScript community challenges Oracle's JavaScript trademark|url=https://www.infoworld.com/article/3532457/javascript-community-challenges-oracles-javascript-trademark.html|work=InfoWorld}}</ref> [[Brendan Eich]], the original creator of JavaScript, was among the over 14,000 signatories who supported the initiative.
== Website client-side usage ==
JavaScript is the dominant [[client-side]] [[scripting language]] of the Web, with
All major [[web browser]]s have a built-in [[JavaScript engine]] that executes the [[Source code|code]] on the user's device.
=== Examples of scripted behavior ===
* Loading new [[web page]] content without reloading the page, via [[Ajax (programming)|Ajax]] or a [[WebSocket]]. For example, [[user (computing)|
* Web page animations, such as fading objects in and out, resizing, and moving them.
* Playing [[browser game]]s.
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* Storing and retrieving data on the user's device, via the [[web storage|storage]] or [[Indexed Database API|IndexedDB]] standards.
===
[[jQuery]] is by far the most-used.<ref name="lib_usage" /> Other notable ones include <!--alphabetically is fair here-->[[Angular (web framework)|Angular]], [[Bootstrap (front-end framework)|Bootstrap]], [[Lodash]], [[Modernizr]], [[React (software)|React]], [[Underscore.js|Underscore]], and [[Vue.js|Vue]].<ref name="lib_usage" /> Multiple options can be used in conjunction, such as jQuery and Bootstrap.<ref>{{cite web |title=Using jQuery with Bootstrap |url=https://clouddevs.com/jquery/web-projects-with-bootstrap/ |website=clouddevs.com |date=10 June 2019 |access-date=17 March 2024}}</ref>
However, the term "Vanilla JS" was coined for websites not using any libraries or frameworks at all, instead relying entirely on standard JavaScript functionality.<ref>{{cite web |date=2020-06-16 |title=Vanilla JS |url=https://vanilla-js.com/ |url-status=live |archive-url=https://web.archive.org/web/20200616052335/https://vanilla-js.com/ |archive-date=June 16, 2020 |access-date=June 17, 2020 |website=vanilla-js.com}}</ref>
== Other usage{{anchor|Server-side_JavaScript|Uses_outside_web_pages}} ==
The use of JavaScript has expanded beyond its [[web browser]] roots. [[JavaScript engine]]s are now
Initial attempts at promoting server-side JavaScript usage were [[Netscape Enterprise Server]] and [[Microsoft]]'s [[Internet Information Services]],<ref>{{cite web |date=December 11, 1998 |title=Server-Side JavaScript Guide |url=https://docs.oracle.com/cd/E19957-01/816-6411-10/contents.htm |url-status=live |archive-url=https://web.archive.org/web/20210311173120/https://docs.oracle.com/cd/E19957-01/816-6411-10/contents.htm |archive-date=March 11, 2021 |access-date=May 8, 2021 |website=oracle.com |publisher=[[Oracle Corporation]]}}</ref><ref>{{cite web|last1=Clinick|first1=Andrew|title=Introducing JScript .NET|url=https://msdn.microsoft.com/en-us/library/ms974588.aspx|website=Microsoft Developer Network|publisher=Microsoft|access-date=April 10, 2018|date=July 14, 2000|quote=[S]ince the 1996 introduction of JScript version 1.0 ... we've been seeing a steady increase in the usage of JScript on the server—particularly in Active Server Pages (ASP)|archive-date=November 10, 2017|archive-url=https://web.archive.org/web/20171110201649/https://msdn.microsoft.com/en-us/library/ms974588.aspx|url-status=live}}</ref> but they were small niches.<ref name="2009server" /> Server-side usage eventually started to grow in the late 2000s, with the creation of [[Node.js]] and [[List of server-side JavaScript implementations|other approaches]].<ref name="2009server">{{cite web |url=https://readwrite.com/2009/12/17/server-side_javascript_back_with_a_vengeance/ |title=Server-Side JavaScript, Back with a Vengeance |date=December 17, 2009 |website=readwrite.com |access-date=July 16, 2016 |author=Mahemoff, Michael |archive-date=June 17, 2016 |archive-url=https://web.archive.org/web/20160617030219/https://readwrite.com/2009/12/17/server-side_javascript_back_with_a_vengeance/ |url-status=live }}</ref>
[[Electron (software framework)|Electron]], [[Apache Cordova|Cordova]], [[React Native]], and other [[application framework]]s have been used to create many applications with behavior implemented in JavaScript. Other non-browser applications include [[Adobe Acrobat]] support for scripting [[PDF]] documents<ref>{{cite web |date=2009-08-07 |title=JavaScript for Acrobat |url=https://www.adobe.com/devnet/acrobat/javascript.html |url-status=live |archive-url=https://web.archive.org/web/20090807065130/https://www.adobe.com/devnet/acrobat/javascript.html |archive-date=August 7, 2009 |access-date=August 18, 2009 |website=adobe.com}}</ref> and [[GNOME Shell]] extensions written in JavaScript.<ref>{{cite web |last=treitter |date=2013-02-02 |title=Answering the question: "How do I develop an app for GNOME?" |url=https://treitter.livejournal.com/14871.html |url-status=live |archive-url=https://web.archive.org/web/20130211032900/https://treitter.livejournal.com/14871.html |archive-date=2013-02-11 |access-date=2013-02-07 |website=livejournal.com}}</ref>
[[Oracle Corporation|Oracle]] used to provide [[Nashorn (JavaScript engine)| Nashorn]], a JavaScript interpreter, as part of their [[JDK|Java Development Kit (JDK)]] API library along with '''jjs''' a command line interpreter as of JDK version 8. It was removed in JDK 15. As a replacement Oracle offered GraalJS which can also be used with the [[OpenJDK]] which allows one to create and reference Java objects in JavaScript code and add runtime scripting in JavaScript to applications written in Java.<ref> {{cite web |last=Ponge |first=Julien |date=2018-04-19 |title=Oracle Nashorn: A Next-Generation JavaScript Engine for the JVM |website=oracle.com |url=https://www.oracle.com/technical-resources/articles/java/jf14-nashorn.html |publisher=Oracle Corporation |access-date=Feb 17, 2025}} </ref><ref>{{cite web |author=<!-- not stated --> |title=Migration Guide from Nashorn to GraalJS |url=https://www.graalvm.org/latest/reference-manual/js/NashornMigrationGuide/ |website=graalvm.org | access-date=Feb 17, 2025}} </ref><ref>{{cite web |author=<!-- not stated --> |title=GraalJS |url=https://www.graalvm.org/latest/reference-manual/js/ |website=|publisher=GraalVM |access-date=Feb 17, 2025}}</ref><ref>{{cite web |author=<!-- not stated --> |title=Java Interoperability | url=https://docs.oracle.com/en/graalvm/enterprise/21/docs/reference-manual/js/JavaInteroperability/|website=oracle.com|publisher=Oracle |access-date=Feb 17, 2025}}</ref>
JavaScript has been used in some [[embedded system]]s, usually by leveraging Node.js.<ref>{{cite web |title=Tessel 2... Leverage all the libraries of Node.JS to create useful devices in minutes with Tessel. |url=https://tessel.io/ |url-status=live |archive-url=https://web.archive.org/web/20210526212559/https://tessel.io/ |archive-date=2021-05-26 |access-date=2021-05-08 |website=tessel.io}}</ref><ref>{{cite web |title=Node.js Raspberry Pi GPIO Introduction |url=https://www.w3schools.com/nodejs/nodejs_raspberrypi_gpio_intro.asp |url-status=live |archive-url=https://web.archive.org/web/20210813192938/https://www.w3schools.com/nodejs/nodejs_raspberrypi_gpio_intro.asp |archive-date=2021-08-13 |access-date=2020-05-03 |website=w3schools.com}}</ref><ref>{{cite web |title=Espruino – JavaScript for Microcontrollers |url=https://www.espruino.com/ |url-status=live |archive-url=https://web.archive.org/web/20200501010722/https://www.espruino.com/ |archive-date=2020-05-01 |access-date=2020-05-03 |website=espruino.com}}</ref>
== Execution ==
===
{{Excerpt|JavaScript engine}}
===
A JavaScript engine must be embedded within a [[runtime system]] (such as a [[web browser]] or a standalone system) to enable scripts to interact with the broader environment. The runtime system includes the necessary APIs for [[input/output]] operations, such as [[computer network|networking]], [[data storage|storage]], and [[computer graphics|graphics]], and provides the ability to import scripts.
JavaScript is a single-[[Thread (computing)|threaded]] language. The runtime processes [[Message (computer science)|messages]] from a [[Queue (abstract data type)|queue]] one at a time, and it calls a [[Subroutine|function]] associated with each new message, creating a [[call stack]] frame with the function's [[Parameter (computer programming)|arguments]] and [[local variable]]s. The call stack shrinks and grows based on the function's needs. When the call stack is empty upon function completion, JavaScript proceeds to the next message in the queue. This is called the [[event loop]], described as "run to completion" because each message is fully processed before the next message is considered. However, the language's [[Concurrency (computer science)|concurrency model]] describes the event loop as [[Asynchronous I/O|non-blocking]]: program I/O is performed using [[Event (computing)|events]] and [[Callback (computer programming)|callback functions]]. This means, for example, that JavaScript can process a mouse click while waiting for a database query to return information.<ref>{{cite web|url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop|title=Concurrency model and Event Loop|website=Mozilla Developer Network|access-date=August 28, 2015|archive-date=September 5, 2015|archive-url=https://web.archive.org/web/20150905045241/https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop|url-status=live}}</ref>
The notable standalone runtimes are [[Node.js]], [[Deno (software)|Deno]], and [[Bun (software)|Bun]].
== Features ==
The following features are common to all conforming ECMAScript implementations unless explicitly specified otherwise. The number of cited reserved words including keywords is 50–60 and varies depending on the implementation.
=== Imperative and structured ===
{{Main|Structured programming}}
JavaScript supports much of the [[structured programming]] syntax from [[C (computer language)|C]] (e.g., <code>if</code> statements, <code>while</code> loops, <code>switch</code> statements, <code>do while</code> loops, etc.). One partial exception is [[scope (computer science)|scoping]]: originally JavaScript only had [[function scoping]] with <code>var</code>; [[block scoping]] was added in ECMAScript 2015 with the keywords <code>let</code> and <code>[[const (computer programming)|const]]</code>. Like C, JavaScript makes a distinction between [[Expression (computer science)|expressions]] and [[Statement (computer science)|statements]]. One syntactic difference from C is [[Defensive semicolon|automatic semicolon insertion]], which allow semicolons (which terminate statements) to be omitted.<ref name="Flanagan2006">{{cite book|last=Flanagan|first=David|title=JavaScript: The Definitive Guide
=== Weakly typed ===
{{
JavaScript is [[Strong and weak typing|weakly typed]], which means certain types are implicitly cast depending on the operation used.<ref name="casting_rules">{{cite web |last=Korolev |first=Mikhail |date=2019-03-01 |title=JavaScript quirks in one image from the Internet |url=https://dev.to/mkrl/javascript-quirks-in-one-image-from-the-internet-52m7 |url-status=live |archive-url=https://web.archive.org/web/20191028204723/https://dev.to/mkrl/javascript-quirks-in-one-image-from-the-internet-52m7 |archive-date=October 28, 2019 |access-date=October 28, 2019 |website=The DEV Community |language=en}}</ref>
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* The binary <code>+</code> operator casts both operands to a string unless both operands are numbers. This is because the addition operator doubles as a concatenation operator
* The binary <code>-</code> operator always casts both operands to a number
* Both unary operators (<code>+</code>, <code>-</code>) always cast the operand to a number. However, <code>+</code> always casts to <code>Number</code> ([[Double-precision floating-point format|binary64]]) while <code>-</code> preserves <code>BigInt</code> ([[Arbitrary-precision arithmetic|integer]])<ref>{{cite web | url=https://github.com/tc39/proposal-bigint/blob/master/ADVANCED.md#dont-break-asmjs | title=Proposal-bigint/ADVANCED.md at master · tc39/Proposal-bigint | website=[[GitHub]] }}</ref>
Values are cast to strings like the following:<ref name="casting_rules" />
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|}
Often also mentioned is <code>{} + []</code> resulting in <code>0</code> (number). This is misleading: the <code>{}</code> is interpreted as an empty code block instead of an empty object, and the empty array is cast to a number by the remaining unary <code>+</code> operator. If
=== Dynamic ===
{{Main|Dynamic
==== Typing ====
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JavaScript includes an <code>[[eval]]</code> function that can execute statements provided as strings at run-time.
=== Object-orientation (prototype-based) ===
Prototypal inheritance in JavaScript is described by [[Douglas Crockford]] as:
{{Blockquote
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}}
In JavaScript, an [[Object (computer science)|object]] is an [[associative array]], augmented with a prototype (see below); each key provides the name for an object [[Property (programming)|property]], and there are two syntactical ways to specify such a name: dot notation (<code>obj.x
==== Prototypes ====
{{Main|Prototype-based programming}}
JavaScript uses [[prototype-based programming|prototypes]] where many other object-oriented languages use [[Class (computer science)|classes]] for [[Inheritance (object-oriented programming)|inheritance]]
class Person {
constructor(name) {
this.name = name;
}
}
class Student extends Person {
constructor(name, id) {
super(name);
this.id = id;
}
}
const bob = new Student("Robert", 12345);
console.log(bob.name); // Robert
</syntaxhighlight>Though the underlying object mechanism is still based on prototypes, the newer syntax is similar to other object oriented languages. Private variables are declared by prefixing the field name with a [[number sign]] (#), and [[Polymorphism (computer science)|polymorphism]] is not directly supported, although it can be emulated by manually calling different functions depending on the number and type of arguments provided.<ref name="JavaScriptNext">{{cite book |last=Ghandi |first=Raju |date=2019 |title=JavaScript Next|___location=New York City |publisher=Apress Media |pages=159–171 |isbn=978-1-4842-5394-6}}</ref>
==== Functions as object constructors ====
Functions double as object constructors, along with their typical role. Prefixing a function call with ''new'' will create an instance of a prototype, inheriting properties and methods from the constructor (including properties from the <code>Object</code> prototype).<ref name="Haverbeke2024">{{Cite book |title=Eloquent JavaScript |last=Haverbeke |first=Marijn |publisher=[[No Starch Press]] |isbn=978-1-71850-411-0 |edition=4th |___location=San Francisco |publication-date=September 2024 |pages=[https://eloquentjavascript.net/Eloquent_JavaScript.pdf#section*.204 97–98] |language=en |url=https://eloquentjavascript.net/Eloquent_JavaScript.pdf |archive-url=https://web.archive.org/web/20250312193854/https://eloquentjavascript.net/Eloquent_JavaScript.pdf |archive-date=2025-03-12 |url-status=live}}</ref> ECMAScript 5 offers the <code>Object.create</code> method, allowing explicit creation of an instance without automatically inheriting from the <code>Object</code> prototype (older environments can assign the prototype to <code>null</code>).<ref>{{cite web|last=Katz|first=Yehuda|title=Understanding "Prototypes" in JavaScript|date=12 August 2011|url=https://yehudakatz.com/2011/08/12/understanding-prototypes-in-javascript/|access-date=April 6, 2013|archive-date=5 April 2013|archive-url=https://web.archive.org/web/20130405154842/https://yehudakatz.com/2011/08/12/understanding-prototypes-in-javascript/|url-status=live}}</ref> The constructor's <code>prototype</code> property determines the object used for the new object's internal prototype. New methods can be added by modifying the prototype of the function used as a constructor.<syntaxhighlight lang="javascript">// This code is completely equivalent to the previous snippet
function Person(name) {
this.name = name;
}
function Student(name, id) {
Person.call(this, name);
this.id = id;
}
var bob = new Student("Robert", 12345);
console.log(bob.name); // Robert</syntaxhighlight>JavaScript's built-in classes, such as <code>Array</code> and <code>Object</code>, also have prototypes that can be modified. However, it's generally considered bad practice to [[Monkey patch|modify built-in objects]], because third-party code may use or inherit methods and properties from these objects, and may not expect the prototype to be modified.<ref>{{cite book |last=Herman |first=David |url=https://books.google.com/books?id=Nz9iAwAAQBAJ&pg=PA125 |title=Effective JavaScript |publisher=Addison-Wesley |year=2013 |isbn=978-0-321-81218-6 |pages=125–127}}</ref>
==== Functions as methods ====
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Unlike in many object-oriented languages, in JavaScript there is no distinction between a function definition and a [[method (computer science)|method]] definition. Rather, the distinction occurs during function calling. When a function is called as a method of an object, the function's local ''this'' keyword is bound to that object for that invocation.
=== Functional ===
{{Main|Functional programming}}
JavaScript [[Subroutine|
==== Lexical closure ====
{{Main|Closure (computer programming)}}
A ''nested'' function is a function defined within another function. It is created each time the outer function is invoked.
In addition, each nested function forms a [[Closure (computer programming)|lexical closure]]: the [[Scope (programming)#Lexical scoping vs. dynamic scoping|lexical scope]] of the outer function (including any constant, local variable, or argument value) becomes part of the internal state of each inner function object, even after execution of the outer function concludes.{{Sfn|Flanagan|2006|p=141}}
==== Anonymous function ====
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JavaScript also supports [[anonymous function]]s.
=== Delegative ===
{{Main|Delegation (object-oriented programming)}}
JavaScript supports implicit and explicit [[Delegation (object-oriented programming)|delegation]].
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{{Main|Role-oriented programming|Traits (computer science)|Mixin}}
JavaScript natively supports various function-based implementations of [[Role-oriented programming|Role]]<ref>[https://peterseliger.blogspot.de/2014/04/the-many-talents-of-javascript.html#the-many-talents-of-javascript-for-generalizing-role-oriented-programming-approaches-like-traits-and-mixins The many talents of JavaScript for generalizing Role-Oriented Programming approaches like Traits and Mixins] {{Webarchive|url=https://web.archive.org/web/20171005050713/https://peterseliger.blogspot.de/2014/04/the-many-talents-of-javascript.html#the-many-talents-of-javascript-for-generalizing-role-oriented-programming-approaches-like-traits-and-mixins |date=2017-10-05 }}, Peterseliger.
==== Object composition and inheritance ====
Whereas explicit function-based delegation does cover [[Object composition|composition]] in JavaScript, implicit delegation already happens every time the prototype chain is walked in order to, e.g., find a method that might be related to but is not directly owned by an object. Once the method is found it gets called within this object's context. Thus [[Inheritance (object-oriented programming)|inheritance]] in JavaScript is covered by a delegation automatism that is bound to the prototype property of constructor functions.
=== Miscellaneous ===
==== Zero-based numbering ====
JavaScript is a [[Zero-based numbering#Usage in programming languages|zero-index]] language.
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{{Main|Regular expression}}
JavaScript supports [[regular expression]]s for text searches and manipulation.{{r|n=Haverbeke2024|p=139}}
===== Promises =====
{{Main|Futures and promises}}
A built-in Promise object provides functionality for handling promises and associating handlers with an asynchronous action's eventual result.
===== Async/await =====
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Async/await allows an asynchronous, non-blocking function to be structured in a way similar to an ordinary synchronous function. Asynchronous, non-blocking code can be written, with minimal overhead, structured similarly to traditional synchronous, blocking code.
=== Vendor-specific extensions ===
Historically, some [[JavaScript engine]]s supported these non-standard features:
* [[List comprehension|array comprehensions]] and generator expressions (like Python)
* concise function expressions (<code>function(args) expr</code>; this experimental syntax predated arrow functions)
* [[ECMAScript for XML]] (E4X), an extension that adds native XML support to ECMAScript (unsupported in Firefox since version 21<ref>{{cite web|title=E4X – Archive of obsolete content |url=https://developer.mozilla.org/en-US/docs/Archive/Web/E4X|website=Mozilla Developer Network|publisher=Mozilla Foundation|date=February 14, 2014|access-date=July 13, 2014|archive-date=July 24, 2014|archive-url=https://web.archive.org/web/20140724100129/https://developer.mozilla.org/en-US/docs/Archive/Web/E4X|url-status=dead}}</ref>)
== Syntax ==
{{Main|JavaScript syntax}}
[[Variable (computer science)|Variables]] in JavaScript can be defined using either the <code>var</code>,<ref>{{cite web | url=https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Statements/var | title=var – JavaScript | publisher=The [[Mozilla Developer Network]] | access-date=December 22, 2012 | archive-date=December 23, 2012 | archive-url=https://web.archive.org/web/20121223162713/https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Statements/var | url-status=live }}</ref> <code>let</code><ref name="moz_let">{{cite web |title=let |url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let |website=MDN web docs |publisher=Mozilla |access-date=June 27, 2018 |ref=moz_let |archive-date=May 28, 2019 |archive-url=https://web.archive.org/web/20190528140803/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let |url-status=live }}</ref> or <code>const</code><ref name="moz_const">{{cite web |title=const |url=https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const |website=MDN web docs |publisher=Mozilla |access-date=June 27, 2018 |ref=moz_const |archive-date=June 28, 2018 |archive-url=https://web.archive.org/web/20180628044054/https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const |url-status=live }}</ref> keywords. Variables defined without keywords will be defined at the global scope.
Arrow functions were first introduced in [[w:ECMAScript#6th Edition – ECMAScript 2015|6th Edition – ECMAScript 2015]]. They shorten the syntax for writing functions in JavaScript. Arrow functions are anonymous, so a variable is needed to refer to them in order to invoke them after their creation, unless surrounded by parenthesis and executed immediately.
Here is an example of JavaScript syntax.
<syntaxhighlight lang="javascript" start="1">
// Declares a function-scoped variable named `x`, and implicitly assigns the
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Note the [[Comment (computer programming)|comments]] in the examples above, all of which were preceded with two [[Slash (punctuation)|forward slashes]].
More examples can be found at the [[wikibooks:JavaScript/Syntax examples|Wikibooks page on JavaScript syntax examples]].
== Security ==
{{See also|Browser security}}
JavaScript and the [[Document Object Model|DOM]] provide the potential for malicious authors to deliver scripts to run on a client computer via the Web. Browser authors minimize this risk using two restrictions. First, scripts run in a [[Sandbox (computer security)|sandbox]] in which they can only perform Web-related actions, not general-purpose programming tasks like creating files. Second, scripts are constrained by the [[same-origin policy]]: scripts from one website do not have access to information such as usernames, passwords, or cookies sent to another site. Most JavaScript-related security bugs are breaches of either the same origin policy or the sandbox.
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[[Content Security Policy]] is the main intended method of ensuring that only trusted code is executed on a Web page.
=== Cross-site
{{Main|Cross-site scripting}}
A common JavaScript-related security problem is [[cross-site scripting]] (XSS), a violation of the [[same-origin policy]]. XSS vulnerabilities occur when an attacker can cause a target Website, such as an online banking website, to include a malicious script in the webpage presented to a victim. The script in this example can then access the banking application with the privileges of the victim, potentially disclosing secret information or transferring money without the victim's authorization.
Some browsers include partial protection against ''reflected'' XSS attacks, in which the attacker provides a URL including malicious script. However, even users of those browsers are vulnerable to other XSS attacks, such as those where the malicious code is stored in a database. Only correct design of Web applications on the server-side can fully prevent XSS.
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XSS vulnerabilities can also occur because of implementation mistakes by browser authors.<ref>{{cite web |url=https://www.mozillazine.org/talkback.html?article=4392 |title=Mozilla Cross-Site Scripting Vulnerability Reported and Fixed – MozillaZine Talkback |website=Mozillazine.org |access-date=February 24, 2017 |archive-date=July 21, 2011 |archive-url=https://web.archive.org/web/20110721230916/http://www.mozillazine.org/talkback.html?article=4392 |url-status=live }}</ref>
===
{{Main|Cross-site request forgery}}
Another cross-site vulnerability is [[cross-site request forgery]] (CSRF). In CSRF, code on an attacker's site tricks the victim's browser into taking actions the user did not intend at a target site (like transferring money at a bank). When target sites rely solely on cookies for request authentication, requests originating from code on the attacker's site can carry the same valid login credentials of the initiating user. In general, the solution to CSRF is to require an authentication value in a hidden form field, and not only in the cookies, to authenticate any request that might have lasting effects. Checking the HTTP Referrer header can also help.
"JavaScript hijacking" is a type of CSRF attack in which a
* requiring an authentication token in the [[POST (HTTP)|POST]] and [[GET (HTTP)|GET]] parameters for any response that returns private information.
=== Misplaced trust in the client ===
Developers of client-server applications must recognize that untrusted clients may be under the control of attackers. The author of an application
* Website authors cannot perfectly conceal how their JavaScript operates because the raw source code must be sent to the client. The code can be [[obfuscated code|obfuscated]], but obfuscation can be reverse-engineered.
* JavaScript form validation only provides convenience for users, not security. If a site verifies that the user agreed to its terms of service, or filters invalid characters out of fields that should only contain numbers, it must do so on the server, not only the client.
* Scripts can be selectively disabled, so JavaScript cannot be relied on to prevent operations such as right-clicking on an image to save it.<ref>{{cite web |last1=Kottelin |first1=Thor |title=Right-click "protection"? Forget about it |url=https://blog.anta.net/2008/06/17/right-click-%E2%80%9Cprotection%E2%80%9D-forget-about-it/ |website=blog.anta.net |access-date=28 July 2022 |archive-url=https://web.archive.org/web/20110809195359/https://blog.anta.net/2008/06/17/right-click-%E2%80%9Cprotection%E2%80%9D-forget-about-it/ |archive-date=9 August 2011 |date=17 June 2008}}</ref>
* It is considered very bad practice to embed sensitive information such as passwords in JavaScript because it can be extracted by an attacker.<ref>{{cite web |last1=Rehorik |first1=Jan |title=Why You Should Never Put Sensitive Data in Your JavaScript |url=https://www.serviceobjects.com/blog/why-you-should-never-put-sensitive-data-in-your-javascript/ |website=ServiceObjects Blog |date=29 November 2016 |publisher=ServiceObjects |access-date=June 3, 2019 |archive-date=June 3, 2019 |archive-url=https://web.archive.org/web/20190603142957/https://www.serviceobjects.com/blog/why-you-should-never-put-sensitive-data-in-your-javascript/ |url-status=live }}</ref>
* [[Prototype pollution]] is a runtime vulnerability in which attackers can overwrite arbitrary properties in an object's prototype.
=== Misplaced trust in developers ===
Package management systems such as [[npm (software)|npm]] and Bower are popular with JavaScript developers. Such systems allow a developer to easily manage their program's dependencies upon other developers' program libraries. Developers trust that the maintainers of the libraries will keep them secure and up to date, but that is not always the case. A vulnerability has emerged because of this blind trust. Relied-upon libraries can have new releases that cause bugs or vulnerabilities to appear in all programs that rely upon the libraries. Inversely, a library can go unpatched with known vulnerabilities out in the wild. In a study done looking over a sample of 133,000 websites, researchers found 37% of the websites included a library with at least one known vulnerability.<ref name="jslibs">{{citation |last1=Lauinger |first1=Tobias |last2=Chaabane |first2=Abdelberi |last3=Arshad |first3=Sajjad |last4=Robertson |first4=William |last5=Wilson |first5=Christo |last6=Kirda |first6=Engin |title=Thou Shalt Not Depend on Me: Analysing the Use of Outdated JavaScript Libraries on the Web |url=https://www.ccs.neu.edu/home/arshad/publications/ndss2017jslibs.pdf |website=Northeastern University |access-date=28 July 2022 |archive-url=https://web.archive.org/web/20170329045344/https://www.ccs.neu.edu/home/arshad/publications/ndss2017jslibs.pdf |archive-date=29 March 2017 |doi = 10.14722/ndss.2017.23414 |date = December 21, 2016|arxiv=1811.00918 |isbn=978-1-891562-46-4 |s2cid=17885720 |url-status=dead}}</ref> "The median lag between the oldest library version used on each website and the newest available version of that library is 1,177 days in ALEXA, and development of some libraries still in active use ceased years ago."<ref name="jslibs" /> Another possibility is that the maintainer of a library may remove the library entirely. This occurred in March 2016 when Azer Koçulu removed his repository from npm. This caused tens of thousands of programs and websites depending upon his libraries to break.<ref>{{cite news |work=Quartz |url=https://qz.com/646467/how-one-programmer-broke-the-internet-by-deleting-a-tiny-piece-of-code/ |title=How one programmer broke the internet by deleting a tiny piece of code |first=Keith |last=Collins |date=March 27, 2016 |access-date=February 22, 2017 |archive-date=February 22, 2017 |archive-url=https://web.archive.org/web/20170222200836/https://qz.com/646467/how-one-programmer-broke-the-internet-by-deleting-a-tiny-piece-of-code/ |url-status=live }}</ref><ref>SC Magazine UK, [https://www.scmagazineuk.com/developers-11-lines-of-deleted-code-breaks-the-internet/article/532050/ Developer's 11 lines of deleted code 'breaks the internet'] {{Webarchive|url=https://web.archive.org/web/20170223041434/https://www.scmagazineuk.com/developers-11-lines-of-deleted-code-breaks-the-internet/article/532050/ |date=February 23, 2017 }}</ref>
=== Browser and plugin coding errors ===
{{Further|Buffer overflow}}
JavaScript provides an interface to a wide range of browser capabilities, some of which may have flaws such as [[buffer overflow]]s. These flaws can allow attackers to write scripts that would run any code they wish on the user's system. This code is not by any means limited to another JavaScript application. For example, a buffer overrun exploit can allow an attacker to gain access to the operating system's [[API]] with superuser privileges.
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In Windows Vista, Microsoft has attempted to contain the risks of bugs such as buffer overflows by running the Internet Explorer process with limited privileges.<ref>{{cite web |url=https://blogs.msdn.com/ie/archive/2006/02/09/528963.aspx |title=Protected Mode in Vista IE7 – IEBlog |website=Blogs.msdn.com |date=February 9, 2006 |access-date=February 24, 2017 |archive-date=January 23, 2010 |archive-url=https://web.archive.org/web/20100123103719/https://blogs.msdn.com/ie/archive/2006/02/09/528963.aspx |url-status=live }}</ref> [[Google Chrome]] similarly confines its page renderers to their own "[[Sandbox (computer security)|sandbox]]".
=== Sandbox implementation errors ===
Web browsers are capable of running JavaScript outside the sandbox, with the privileges necessary to, for example, create or delete files. Such privileges are not intended to be granted to code from the Web.
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[[Microsoft Windows]] allows JavaScript source files on a computer's hard drive to be launched as general-purpose, non-sandboxed programs (see: [[Windows Script Host]]). This makes JavaScript (like [[VBScript]]) a theoretically viable vector for a [[Trojan horse (computing)|Trojan horse]], although JavaScript Trojan horses are uncommon in practice.<ref>For one example of a rare JavaScript Trojan Horse, see Symantec Corporation, [https://www.symantec.com/security_response/writeup.jsp?docid=2003-100111-0931-99 JS.Seeker.K] {{Webarchive|url=https://web.archive.org/web/20110913210848/http://www.symantec.com/security_response/writeup.jsp?docid=2003-100111-0931-99 |date=2011-09-13 }}</ref>{{failed verification|date=March 2017}}
=== Hardware vulnerabilities ===
In 2015, a JavaScript-based proof-of-concept implementation of a [[rowhammer]] attack was described in a paper by security researchers.<ref>{{cite arXiv | eprint = 1507.06955 | title = Rowhammer.js: A Remote Software-Induced Fault Attack in JavaScript | date = July 24, 2015 | last1 = Gruss | first1 = Daniel | last2 = Maurice | first2 = Clémentine | last3 = Mangard | first3 = Stefan | class = cs.CR }}</ref><ref>{{cite news |work=Motherboard |publisher=[[Vice (magazine)|Vice]] |title=Rowhammer.js Is the Most Ingenious Hack I've Ever Seen |first=Alix |last=Jean-Pharuns |date=July 30, 2015 |url=https://
In 2017, a JavaScript-based attack via browser was demonstrated that could bypass [[Address space layout randomization|ASLR]]. It is called "ASLR⊕Cache" or AnC.<ref>[https://www.vusec.net/projects/anc/ AnC] {{Webarchive|url=https://web.archive.org/web/20170316055626/https://www.vusec.net/projects/anc/ |date=2017-03-16 }} VUSec, 2017</ref><ref>[https://arstechnica.com/security/2017/02/new-aslr-busting-javascript-is-about-to-make-drive-by-exploits-much-nastier/ New ASLR-busting JavaScript is about to make drive-by exploits much nastier] {{Webarchive|url=https://web.archive.org/web/20170316024419/https://arstechnica.com/security/2017/02/new-aslr-busting-javascript-is-about-to-make-drive-by-exploits-much-nastier/ |date=2017-03-16 }} Ars Technica, 2017</ref>
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In 2018, the paper that announced the [[Spectre (security vulnerability)|Spectre]] attacks against Speculative Execution in Intel and other processors included a JavaScript implementation.<ref>[https://spectreattack.com/spectre.pdf Spectre Attack] {{Webarchive|url=https://web.archive.org/web/20180103225843/https://spectreattack.com/spectre.pdf |date=2018-01-03 }} Spectre Attack</ref>
== Development tools ==
Important tools have evolved with the language.
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* Many [[text editor]]s have syntax highlighting support for JavaScript code.
== Related technologies ==
=== Java ===
A common misconception is that JavaScript is directly related to [[Java (programming language)|Java]].<!-- While one is intentionally similar to the other, they're different. (Previously the misconception sentence said "JavaScript is similar to Java" but that's not a misconception) --> Both indeed have a C-like syntax (the C language being their most immediate common ancestor language). They are also typically [[Sandbox (computer security)|sandboxed]], and JavaScript was designed with Java's syntax and standard library in mind. In particular, all Java keywords were reserved in original JavaScript, JavaScript's standard library follows Java's naming conventions, and JavaScript's {{code|lang=javascript|code=Math}} and {{code|lang=javascript|code=Date}} objects are based on classes from Java 1.0.<ref name="popularity">{{cite web | url=https://brendaneich.com/2008/04/popularity/ | title=Popularity | first=Brendan | last=Eich | author-link=Brendan Eich | date=April 3, 2008 | access-date=January 19, 2012 | archive-date=July 3, 2011 | archive-url=https://web.archive.org/web/20110703020955/https://brendaneich.com/2008/04/popularity/ | url-status=live }}</ref>
Both languages first appeared in 1995, but Java was developed by [[James Gosling]] of Sun Microsystems and JavaScript by [[Brendan Eich]] of Netscape Communications.
The differences between the two languages are more prominent than their similarities. Java has [[static typing]], while JavaScript's typing is [[Dynamic typing|dynamic]]. Java is loaded from [[Compiler|compiled]] bytecode, while JavaScript is loaded as human-readable source code. Java's objects are [[Class-based programming|class-based]], while JavaScript's are [[Prototype-based programming|prototype-based]]. Finally, Java did not support functional programming until Java 8, while JavaScript has done so from the beginning, being influenced by [[Scheme (programming language)|Scheme]].
===
[[JSON]] is a data format derived from JavaScript; hence the name JavaScript Object Notation. It is a widely used format supported by many other programming languages.
=== Transpilers ===
Many websites are JavaScript-heavy, so [[transpiler]]s have been created to convert code written in other languages, which can aid the development process.<ref name="transpilers">{{cite web |title=List of languages that compile to JS |first=Jeremy |last=Ashkenas |website=[[GitHub]] |author-link=Jeremy Ashkenas |url=https://github.com/jashkenas/coffeescript/wiki/List-of-languages-that-compile-to-JS |access-date=February 6, 2020 |archive-date=January 31, 2020 |archive-url=https://web.archive.org/web/20200131233044/https://github.com/jashkenas/coffeescript/wiki/List-of-languages-that-compile-to-JS |url-status=live }}</ref>
[[TypeScript]] and [[CoffeeScript]] are two notable languages that transpile to JavaScript.
=== WebAssembly ===
[[WebAssembly]] is a newer language with a [[bytecode]] format designed to complement JavaScript, especially the performance-critical portions of [[web page]] scripts. All of the major [[JavaScript engine]]s support WebAssembly,<ref>{{cite web|url=https://visualstudiomagazine.com/articles/2017/11/06/edge-webassembly.aspx|title=Edge Browser Switches WebAssembly to 'On' -- Visual Studio Magazine|website=Visual Studio Magazine|access-date=2018-02-09|archive-date=2018-02-10|archive-url=https://web.archive.org/web/20180210002432/https://visualstudiomagazine.com/articles/2017/11/06/edge-webassembly.aspx|url-status=live}}</ref> which runs in the same [[Sandbox (computer security)|sandbox]] as regular JavaScript code.
[[asm.js]] is a subset of JavaScript that served as the forerunner of WebAssembly.<ref>{{cite web | url=https://asmjs.org/faq.html | title=frequently asked questions | publisher=asm.js | access-date=April 13, 2014 | archive-date=June 4, 2014 | archive-url=https://web.archive.org/web/20140604012024/https://asmjs.org/faq.html | url-status=live }}</ref>
== Notes ==
{{notelist}}
==
{{Reflist}}
== Further reading ==
{{See also|ECMAScript#External_links|l1=ECMAScript Specification Documents}}
* {{cite book|last=Flanagan
* {{Cite book |title=Eloquent JavaScript |last=Haverbeke |first=Marijn |publisher=[[No Starch Press]] |isbn=978-1-71850-411-0 |edition=4th |___location=San Francisco |publication-date=2024 |url=https://eloquentjavascript.net/Eloquent_JavaScript.pdf |archive-url=https://web.archive.org/web/20250312193854/https://eloquentjavascript.net/Eloquent_JavaScript.pdf |archive-date=2025-03-12 |url-status=live}}
* {{cite book|last=Zakas
== External links ==
{{
{{Spoken Wikipedia|En-JavaScript.ogg|date=August 20, 2013}}
* [https://javascript.info/ The Modern JavaScript Tutorial]. A community maintained continuously updated collection of tutorials on the entirety of the language.
* {{cite web |url=https://www.pldi21.org/prerecorded_hopl.12.html |title=JavaScript: The First 20 Years |access-date=2022-02-06}}
{{JavaScript}}
{{ECMAScript}}
{{Web browsers|fsp}}
{{NodeJs}}
{{Programming languages}}
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