According to the The Windows Internet Explorer Weblog, "The IE9 Platform Preview includes the first release of our new JavaScript engine, codenamed Chakra, which fundamentally changes the performance characteristics of JavaScript inside Internet Explorer 9. Chakra includes a new JavaScript compiler that compiles JavaScript source code into high-quality native machine code, a new interpreter for executing script on traditional web pages, and improvements to the JavaScript runtime and libraries."

Allen Wirfs-Brock, Microsoft JavaScript Language Architect, recently posted an interesting discussion about how the development team working on the Chakra engine decides whether they will implement features that aren't included in a standards specification, with the aim of ensuring optimum interoperability. Chakra is being developed in careful accordance with the ECMAScript 5 (ES5) specification, but there are subtleties involved in determining what, for instance, constitutes a "real" regular expression.

Among the topics Wirfs-Brock covers in his post are "consensus features," the treatment of getter and setter methods, and the fact that, at present, IE9 will not support const declarations.

The piece is an interesting explanation of how a development team handles the gray areas in anticipating standardization when working on an update, and offers insight into the analysis process that goes on behind-the-scenes when deciding whether to support certain features.

To read the complete post, see Chakra: Interoperability Means More Than Just Standards.