This does not seem to work. It needs to be in an IIFE with a "use strict" statment, but even then, I run into this bug on Chrome: https://code.google.com/p/v8/issues/detail?id=3953
It will work in Firefox once they enable `let` without specifying the script version.
It will work in Chrome once they fix for-of and once they make `let` work outside of strict mode.