ECMAScript engine

A JavaScript engine is a program or interpreter which executes JavaScript code. A JavaScript engine may be a traditional interpreter, or it may utilize just-in-time compilation to bytecode in some manner. Although there are several uses for a JavaScript engine, it is most commonly used in Web browsers.

Before the second browser war in 2008-2009, JavaScript engines (also termed JavaScript interpreter or JavaScript implementation) were simply interpreters that read and executed JavaScript source code.

The first JavaScript engine was created by Brendan Eich at Netscape Communications Corporation for the Netscape Navigator web browser. The engine, code named SpiderMonkey, is implemented in C++. It has since been updated (in JavaScript 1.5) to conform to ECMA-262 Edition 3. The Rhino engine, created primarily by Norris Boyd (also at Netscape) is a JavaScript implementation in Java. Like SpiderMonkey, Rhino is ECMA-262 Edition 3 compliant. Applications of the technology include Apple Safari 4's Nitro, Google Chrome's V8 and Mozilla Firefox 3.5's TraceMonkey.

By far the most common host environment for JavaScript is a web browser. Web browsers typically use the public application programming interface (API) to create "host objects" responsible for reflecting the Document Object Model (DOM) into JavaScript.

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