Saturday, June 28, 2014

JavaScript Engine : V8

A JavaScript engine is process virtual machine which interprets and executes JavaScript. Although there are several uses for a JavaScript engine, it is most commonly used in web browsers. Web browsers typically use the public application programming interface (API) to create "host objects" responsible for reflecting the Document Object Model (DOM) into JavaScript.
The web server is another common application of the engine. A JavaScript web server exposes host objects representing an HTTP request and response objects, which a JavaScript program then manipulates to dynamically generate web pages.


The V8 JavaScript Engine is an open source JavaScript engine developed by Google for the Google Chrome web browser. V8 compiles JavaScript to native machine code (IA-32, x86-64, ARM, or MIPS ISAs) before executing it, instead of more traditional techniques such as interpreting bytecode or compiling the whole program to machine code and executing it from a filesystem. The compiled code is additionally optimized (and re-optimized) dynamically at runtime, based on heuristics of the code's execution profile. Optimization techniques used include inlining, elision of expensive runtime properties, and inline caching, among many others.
V8 is a new JavaScript engine specifically designed for fast execution of large JavaScript applications. It handles memory allocation for objects, and garbage collects objects it no longer needs. V8's stop-the-world, generational, accurate garbage collector is one of the keys to V8's performance.
There are three key areas to V8's performance:
  • Fast Property Access
  • Dynamic Machine Code Generation
  • Efficient Garbage Collection
Some Facts about V8:
  • V8 is Google's open source JavaScript engine. 
  • V8 is written in C++ and is used in Google Chrome, the open source browser from Google. 
  • V8 can run standalone, or can be embedded into any C++ application. 
  • The garbage collector of V8 is a generational incremental collector.
  • V8 assembler is based on the Strongtalk assembler.
  • V8 is intended to be used both in a browser and as a standalone high-performance engine that can be integrated into independent projects, for example server-side JavaScript in Node.js, or client side JavaScript in .NET/Mono using V8.NET.

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