What differences are between javascript in Firefox 4 and IE9

Question

IE9 supports ecma-262 edition 5 (http://en.wikipedia.org/wiki/ECMAScript) and Firefox 4 is javascript 1.8.5 (https://developer.mozilla.org/en/JavaScript/New_in_JavaScript/1.8.5).

How compliant is IE9 with ECMA-262 edition 5 and is that the same as ECMAScript5?

I expect there are more differences than similarities between the two javascript engines, but I am curious how close IE9 has moves toward Firefox, in terms of new javascript functionality.

Answer 1

IE 9 pretty much supports ECMAScript 5, except for the Strict Mode.

ECMAScript 5 support in browsers compared by @kangax http://kangax.github.com/es5-compat-table/ (note that the table shows only existence, not functionality)

Definitely there'll differences between the JavaScript Engines - Chakra, SpiderMonkey, V8 and others, as the implementations will vary and their support for non-standard features http://kangax.github.com/es5-compat-table/non-standard/