After inconspicuously lurking within Web sites' code for more than a decade, JavaScript has emerged to become a key battleground in a second era of Web browser wars. JavaScript, which lets developers create everything from basic Web site menus to online spreadsheet applications, was born in the mid-1990s when Microsoft's Internet Explorer challenged the incumbent browser, Netscape's Navigator. IE won that war, but now it faces its own challenge from the heir to the Navigator throne, Mozilla's Firefox, along with upstarts including Google's Chrome, Apple's Safari, and Opera. All the challengers tout JavaScript performance as a major part of their competitive attack--even to the point of naming their JavaScript engines built into their browsers: Chrome's V8, Firefox's TraceMonkey, Opera's Futhark and upcoming Carakan, and Safari's newly branded Nitro, which is Apple's version of WebKit's Squirrelfish.

Microsoft's tests of page-loading speeds gave it the edge over Chrome and Firefox. But page-loading speed isn't everything
(Credit: Microsoft)Though IE lags all these rivals in JavaScript performance, Microsoft does care about performance overall and JavaScript performance specifically. Even as Microsoft launched a brand-new browser version, Internet Explorer 8, on Thursday, however, it's also clear the company has a big difference of opinion about the matter.

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