ECMAScript 4 is destined to be the next generation of JavaScript, eventually replacing the current version of what is likely the most widely-used programming language today.

The ECMAScript 4 standard itself is still in development, but there are already a large number of new features that the final spec will certainly provide, such as optional static typing, native support for XML, and a combination of object-oriented and functional programming facilities. In many ways, the designers of ECMAScript 4 aimed to fix most of the problems that plagued JavaScript, while also keeping JavaScript's best features, such as higher-order functions and closures.

JQuery creator John Resig has been participating in the ECMAScript 4 efforts, and in a recent blog post reviews the current implementations of the spec.

Predictably, the ECMAScript 4 reference implementation provides the most new features, followed closely by Tamarin, a join VM project between Mozilla and Adobe. Included in the list is the Mbedthis commercial implementation focused on embedded Web servers, as is Mozilla's Spidermonkey, and the Java-based ECMAScript implementation, Rhino.

Resig notes that,

I went through and attempted to compile as many bugs and features as possible, as stated by the ECMAScript 4 specification and double-check them against all the actively-maintained implementations... I think it's fascinating to note that there [are] 3 implementations that already have over 25% of all the new features in the language implemented.

If you've looked at the ECMAScript 4 language, what new language features do you like the most?