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TraceMonkey

SpiderMonkey
Developer(s) Mozilla Foundation / Mozilla Corporation
Development status Active
Written in C/C++
Operating system Cross-platform
Platform IA-32, x86-64, ARM, MIPS, SPARC
Type JavaScript engine
License MPL 2.0
Website developer.mozilla.org/en/SpiderMonkey

SpiderMonkey is the code name for the first JavaScript engine, written by Brendan Eich at Netscape Communications, later released as open source and currently maintained by the Mozilla Foundation. SpiderMonkey provides JavaScript support for Mozilla Firefox and various embeddings such as the GNOME 3 desktop.

Eich "wrote JavaScript in ten days" in 1995, having been "recruited to Netscape with the promise of 'doing Scheme' in the browser". (The idea of using Scheme was abandoned when "engineering management [decided] that the language must ‘look like Java’".) In the fall of 1996, Eich, needing to "pay off [the] substantial technical debt" left from the first year, "stayed home for two weeks to rewrite Mocha as the codebase that became known as SpiderMonkey". The name SpiderMonkey may have been chosen as a reference to the movie Beavis and Butt-head Do America, in which the character Tom Anderson mentions that the title characters were "whacking off like a couple of spider monkeys." In 2011, Eich transferred management of the SpiderMonkey code to Dave Mandelin.

TraceMonkey was the first JIT compiler written for the JavaScript language. The compiler was first released as part of SpiderMonkey in Firefox 3.5, providing "performance improvements ranging between 20 and 40 times faster" than the baseline interpreter in Firefox 3.

Instead of compiling whole functions, TraceMonkey was a tracing JIT, which operates by recording control flow and data types during interpreter execution. This data then informed the construction of Trace Trees, highly specialized paths of native code.


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