A JavaScript engine is a

software component Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...

that executes

JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of websites use JavaScript on the client side for webpage behavior, of ...

code. The first JavaScript

engines An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...

were mere interpreters, but all relevant modern engines use

just-in-time compilation In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is a way of executing computer code that involves compilation during execution of a program (at run time) rather than before execution. This may co ...

for improved performance. JavaScript engines are typically developed by

web browser A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used o ...

vendors, and every major browser has one. In a browser, the JavaScript engine runs in concert with the rendering engine via the

Document Object Model The Document Object Model (DOM) is a cross-platform and language-independent interface that treats an XML or HTML document as a tree structure wherein each node is an object representing a part of the document. The DOM represents a document wi ...

. The use of JavaScript engines is not limited to browsers. For example, the

V8 engine A V8 engine is an eight-cylinder piston engine in which two banks of four cylinders share a common crankshaft and are arranged in a V configuration. The first V8 engine was produced by the French Antoinette company in 1904, developed and u ...

is a core component of the Node.js and Deno

runtime system In computer programming, a runtime system or runtime environment is a sub-system that exists both in the computer where a program is created, as well as in the computers where the program is intended to be run. The name comes from the compile t ...

s. Since

ECMAScript ECMAScript (; ES) is a JavaScript standard intended to ensure the interoperability of web pages across different browsers. It is standardized by Ecma International in the documenECMA-262 ECMAScript is commonly used for client-side scripting o ...

is the standardized specification of JavaScript, ECMAScript engine is another name for these engines. With the advent of WebAssembly, some engines can also execute this code in the same sandbox as regular JavaScript code.

History

The first JavaScript engine was created by

Brendan Eich Brendan Eich (; born July 4, 1961) is an American computer programmer and technology executive. He created the JavaScript programming language and co-founded the Mozilla project, the Mozilla Foundation, and the Mozilla Corporation. He served ...

in 1995 for the

Netscape Navigator Netscape Navigator was a web browser, and the original browser of the Netscape line, from versions 1 to 4.08, and 9.x. It was the flagship product of the Netscape Communications Corp and was the dominant web browser in terms of usage share in ...

. It was a rudimentary interpreter for the nascent language Eich invented. (This evolved into the

SpiderMonkey SpiderMonkey is the first JavaScript engine, written by Brendan Eich at Netscape Communications, later released as open source and currently maintained by the Mozilla Foundation. It is used in the Firefox web browser. History Eich "wrote ...

engine, still used by the

Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...

browser.) The first modern JavaScript engine was V8, created by

Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...

for its Chrome browser. V8 debuted as part of Chrome in 2008, and its performance was much better than any prior engine. The key innovation was

, which can significantly improve execution times. Other browser vendors needed to overhaul their interpreters to compete.

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...

developed the Nitro engine for its Safari browser, which had 30% better performance than its predecessor.

Mozilla Mozilla (stylized as moz://a) is a free software community founded in 1998 by members of Netscape. The Mozilla community uses, develops, spreads and supports Mozilla products, thereby promoting exclusively free software and open standards, w ...

leveraged portions of Nitro to improve its own SpiderMonkey engine. Since 2017, these engines have added support for WebAssembly. This enables the use of pre-compiled executables for performance-critical portions of page scripts.

Notable engines

* V8 from

is the most used JavaScript engine. Google Chrome and the many other Chromium-based browsers use it, as do

applications Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...

built with CEF,

Electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

, or any other framework that embeds Chromium. Other uses include the Node.js and Deno

s. *

is developed by

for use in

and its forks. The

GNOME Shell GNOME Shell is the graphical shell of the GNOME desktop environment starting with version 3, which was released on April 6, 2011. It provides basic functions like launching applications, switching between windows and is also a widget engine. ...

uses it for extension support. * JavaScriptCore is

's engine for its Safari browser. Other

WebKit WebKit is a browser engine developed by Apple and primarily used in its Safari web browser, as well as on the iOS and iPadOS version of any web browser. WebKit is also used by the BlackBerry Browser, PlayStation consoles beginning from the P ...

-based browsers also use it. KJS from KDE was the starting point for its development. * Chakra is the engine of the

Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, commonly abbreviated IE or MSIE) is a series of graphical web browsers developed by Microsoft which was used in the Windows line of operating systems ( ...

browser. It was also forked by

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...

for the original

Edge Edge or EDGE may refer to: Technology Computing * Edge computing, a network load-balancing system * Edge device, an entry point to a computer network * Adobe Edge, a graphical development application * Microsoft Edge, a web browser developed ...

browser, but Edge was later rebuilt as a Chromium-based browser and thus now uses V8.

References

{{DEFAULTSORT:JavaScript engine

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...