Apple is apparently working on significant improvements to JavaScript performance for its Safari browser, as shown by the inclusion of accelerator upgrades in recent builds of WebKit, reports InfoWorld.

WebKit is the open source browser engine created by Apple and which serves as the basis for Safari, and the new upgrades to WebKit's "Nitro" JavaScript engine are known as "FTLJIT". With the upgrades, WebKit's JavaScript engine would become more competitive with Google's V8 and Mozilla's SpiderMonkey engines.

FTLJIT is still considered experimental, so although it's being made available in the OS X port of WebKit by default, it's not actually turned on yet -- it has to be enabled through command-line flags. One attribute that could make FTLJIT stand out from the pack all the more is how well it runs JavaScript code that is not specifically optimized for [Mozilla's] asm.js. Every JavaScript engine will run asm.js code, but only Mozilla's SpiderMonkey honors asm.js-specific optimizations, and right now no other browser maker has elected to follow Mozilla's lead.

The report notes that speed tests are showing WebKit with FTLJIT enabled outperforming Chrome, while Firefox still tops the charts when using asm.js-optimized benchmark tests.

JavaScript has been a key technology for web browsers for many years, facilitating a variety of user interactions with web pages such as dynamic loading of content without reloading pages and handling page animations and other media. Because JavaScript code embedded on a website is run inside the user's browser when the page is loaded, the efficiency of the browser's JavaScript engine can have a significant impact on the user experience as JavaScript implementations become increasingly complex.

It is unclear whether Apple is targeting OS X 10.10 for these JavaScript improvements, but with them only being enabled in the OS X version of WebKit, it appears that there is still substantial work to be done.