How do I know which version of Javascript I'm using?

I'm just reading this documentation about Javascript 1.2, but I'm wondering which version of Javascript is being used in the most popular browsers.

http://www.tutorialspoint.com/javascript/javascript_nested_functions.htm

Wikipedia (or rather, the community on Wikipedia) keeps a pretty good up-to-date list here.

• Most browsers are on 1.5 (though they have features of later versions)
• Mozilla progresses with every dot release (they maintain the standard so that's not surprising)
• Firefox 4 is on JavaScript 1.8.5
• The other big off-the-beaten-path one is IE9 - it implements ECMAScript 5, but doesn't implement all the features of JavaScript 1.8.5 (not sure what they're calling this version of JScript, engine codenamed Chakra, yet).