Support of different Javascript versions in browsers

Surfing the MDC docs here, I've noticed there are quite a few versions of javascript (1.6 to 1.8.5).

I was wondering:

1. Is there any online reference for Browser / Javascript version supported ?

2. Is there any practical application for the use of different javascript versions ? According to MDC you need to do something like this to use them:

<script type="application/javascript;version=1.7"/>

Which I haven't seen in any website IIRC.

Thanks!

1) Yes, on Wikipedia is a nice list: http://en.wikipedia.org/wiki/JavaScript#Version_history

2) For websites it's not a good idea to use newer versions of Javascript, but for plugins for newer browsers it can be helpful. For example, I'm using the forEach function in plugins for Google Chrome

1. Wikipedia has a pretty good chart of browser/versions, check it out here.
   • Note: JavaScript isn't the only ECMAScript implementation, and JavaScript (the standard maintained by Mozilla) and JavaScript the language (more general, sometimes inaccurately used, term) are not the same thing, for example IE's implementation is called JScript.
2. Not that I've ever seen in anything practical/widespread...you'd have to be doing something pretty specific/specialized for it to have any merit, imo.