Scala dev here who sometimes needs to do some JS (though haven't worked with ember). I feel your pain! Static typing and functional programming certainly make ones life easier once a project becomes bigger.

Anyway, for future reference, you may want to learn how to use the JS debugger (both Chrome and Firefox are quite good). You could have set a break/watchpoint on the variable 'foo'. Once it has changed, you can inspect the stack and would have found that the set('bar', ...) method was involved. Should be much quicker than printf-debugging...