Tamarin

I guess you all heard that MacromediaAdobe donated
their JIT compiler version of JavaScript to Mozilla. Tamarin is the JIT
for Action Script 3 (AS3) which is a version of ECMAScript 3rd Edition.
Using a JIT should improvement of JavaScript by at least 10x. This is of
course very good news. However a lot of people seem to think that this
will improve their DHTML applications by a factor 10 as well. This is of course not the
case since JavaScript is not the bottle neck in DHTML. The time spent in
pure JavaScript is less than 10% (number taken out of thin air). The
main bottle necks in an application today is COM/XPCOM, DOM and reflows.

Another misunderstanding on a lot of blogs is that AS3 is an
implementation of JavaScript 2 (ECMAScript 4th Edition). This is not the
case. AS3 has a lot of features that are in the working drafts of JS2
but it also misses a lot of things that JS1.7 already supports.

JScript5.x < JavaScript 1.5 < JavaScript 1.7 < JScript.NET < AS3 < JS2

This is of course not a linear relation but you get the point. If you remove the class and type system then AS3 and JScript.NET are less similar to JS2 than JS1.5.