SpiderMonkey (JavaScript engine)

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SpiderMonkey is the code name for the first ever JavaScript engine, written by Brendan Eich at Netscape Communications, later released as open source and now maintained by the Mozilla Foundation.



SpiderMonkey is written in C and contains a compiler, interpreter, decompiler, garbage collector, and standard classes. It does not itself provide host environments such as Document Object Model (DOM).

SpiderMonkey and its sister engine Rhino have implemented support for the ECMAScript for XML (E4X) standard.


It is intended to be embedded in other applications that provide host environments for JavaScript. The most popular applications are Mozilla Firefox and the Mozilla Application Suite/SeaMonkey, along with Adobe Acrobat and Adobe Reader. SpiderMonkey is also the JavaScript engine for Yahoo! Widgets (formerly known as "Konfabulator") and UOX3, an Ultima Online server emulator. A rather popular and creative utilization of the SpiderMonkey JavaScript engine is the open source Sphere suite of applications primarily intended to aid in the design of role-playing games. Parts of SpiderMonkey are used in the Wine project's Jscript (re-)implementation.[1] The Methabot web crawler uses SpiderMonkey in a multi-threaded environment for running user-provided filetype and URL parsers. It is also used in CouchDB database system written in Erlang - JavaScript is used for defining maps, filters, reduce functions and viewing data for example in HTML format. FreeSWITCH, open-source telephony engine, uses SpiderMonkey to provide users with ability to write call management scripts in JavaScript. Several large organizations have been known to use SpiderMonkey for managing their JavaScript for front-end applications.


Mozilla has added optimization using "Trace Trees" to SpiderMonkey. Released June 30th, 2009, Firefox 3.5 includes this new optimization technique which offers "performance improvements ranging between 20 and 40 times faster in some cases".[2]

See also


  1. wine-cvs mailing list, September 16, 2008: “jscript: Added regular expression compiler based on Mozilla regexp implementation”
  2. http://arstechnica.com/news.ars/post/20080822-firefox-to-get-massive-javascript-performance-boost.html

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