Apple revises WebKit JavaScript handling, sees speed gains
updated 01:15 am EST, Fri March 2, 2012
Will benefit all WebKit-based browsers over time
A recent hire in Apple's WebKit development team has come up with a new Low-Level Interpreter (LLInt) that can do much more processing of JavaScript code in WebKit's JavaScriptCore before handing it off to the Just-In-Time (JIT) compiler or bytecode virtual machine, realizing a speed gain of over 200 percent compared to the current model. The "triple-tier" approach will result in more fluid animations and faster programatic web applications, widgets and more.
The work appears to have been done by Filip Pizlo, whom AppleInsider reports just joined Apple's WebKit group in December. The code change has been released to the open-source WebKit group and should benefit any WebKit-dependent browser, such as Safari, Chrome, iCab, Steam's ingame browser, OmniWeb, iOS and WebOS. The changes will not appear in browsers immediately but may show up as early as the next significant release of Safari, expected to be version 5.2.
The new interpreter is said to be "2-2.5 times faster than our old interpreter on SunSpider, V8 and Kraken [benchmarks]," the report says, and gets "double digit improvement on real-world websites" due to the reduction in the amount of code that must be translated by the JIT or bytecode virtual machine. While the optimization does not aid any non-JavaScript parts of the web browsing process, the JavaScript component has become increasingly important for rich application and media experiences through web browsers and is a prime area for optimization, having already seen a number of multiple-time improvements in recent years.
The V8 benchmark referred to in the report refers to Google's competing JavaScript engine, which converts JavaScript to native code before running it. Google has been attempting to move away from JavaScript towards its own web programming language called Dart, but has met with strong resistance from other industry players, much as it has when it chose to push WebM over H.264 and Flash over HTML5, though it has backtracked somewhat on the latter as Adobe has pulled out of mobile Flash.
