John Resig has posted a whitepaper outlining the new features in ECMAScript4 (aka the Javascript standard), how it differs from ECMAScript3, and the rationale for any incompatibilities.
Many of the features have already made their way into Opera and Firefox, which is at Javascript 1.7 level. ES3 is equivalent to JS1.3, and ES4 is the basis for forthcoming JS2.
I look forward to optional strict typing, multiline strings, comprehensions, and generators making their way into browsers. A lot of the new features make Javascript more like Python without losing all the nice things tabout Javascript.
Leo on Tech 