== and != do coercion, i.e. '2' === 2. 

Douglas Crockford describes these as the evil twins of === and ==. There's a detailed summary [here](http://stackoverflow.com/questions/359494/does-it-matter-which-equals-operator-vs-i-use-in-javascript-comparisons). In theory === could also result in better performance.

I understand the arguments pro and con, but TBH I've standardised on === mostly so linting tools like [jshint](http://jshint.com) don't grumble!

There's actually nothing about this in the [Google Style Guide](https://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml).