While I was away these past couple weeks two important papers were released that detail some of the changes that are coming about in ECMAScript 4.

The first is a white paper (40 pages, PDF) that paints a wide stroke, covering nearly all new features introduced in the language, to some degree or another. Probably the most important part is looking at the goals for the language:

Compatible with ECMAScript 3

Suitable to developing large systems

Allow for reusable libraries

Merge previous efforts (ActionScript)

Fix ECMAScript 3 bugs

Keep it usable for small programs

Give it a read and test out the code against the reference implementation (a lot of it will work, but it’s only about 70% of the way there). By the way, the reference implementation was also updated (version M1) – you should find it to be much less buggy now, they’ve been making good progress on it.

The second document is a detailed one specifying all the backwards compatibility changes that will be made in ECMAScript 4. The changes that have been outlined are specific, but generally quite safe (the most significant ones were detailed in my previous blog post on the subject).

Let me know if you have questions about the contents of either of the documents and I’ll do my best to try and answer them.