The development of ECMAScript 4 is moving into an important phase: the implementors are making good on their word and are starting to implement the ECMAScript 4 proposals. Many of the features have been well thought out by this point and the implementors are working hard to integrate the necessary changes into their engines.

A couple important pieces are coming along but the most critical of which is the ECMAScript 4 Reference Implementation. They've released [1] a second milestone release. You can find a copy of the implementation on the ECMAScript download page [2].

An important list of features is starting to become available in the reference implementation:

Implemented, may have bugs:

• classes and interfaces
• namespaces
• pragmas
• let, const, let-const
• iterators
• enumerability control
• type expressions / definitions / annotations
• runtime type checks ("standard mode")
• nullability
• destructuring assignment
• slice syntax
• hashcode
• catchalls
• map & vector
• date & time improvements
• meta objects
• static generics
• string trim
• typeof
• globals
• expression closures
• name objects
• type operators (is / to / cast / wrap)

Implemented and partly working, but still in flux / work to do:

• inheritance checking
• strict mode
• type parameters
• structural types
• numbers & decimal
• getters & setters (structural part is incomplete)
• packages

Now a full feature list [3] is also being worked on by all of the implementors (as I mentioned previously [4]). This list is going to serve as the starting point for many implementors especially when they decide which features to implement.

Adobe has also taken a step and has outlined [5] (note the column with green/red/etc.) where they stand on all of the ECMAScript 4 proposals. They also took the time to outline their position [6] on the proposals that they're (currently) declining to implement.

This is a really important step in the development of the language. The implementors are staking their ground and are working hard to make sure that a solid language comes out at the end - especially one that is universally implemented. Both Google and Apple have also been participating the ECMAScript 4 mailing list, asking a lot of good questions, as they look towards creating their own ES4 implementations (in Rhino and WebKit, respectively).

Pretty much everyone can agree that a lack of dialog between implementors would surely cause problems - but that does not appear to be the case, here. Because of this openness and solid dialog ECMAScript 4 looks to have a strong future.