Chrome is too smart for its own good

Run the following into the chrome console:

(function(){
    var foo = 3;
    (function(){
        debugger
    })();
})(); <!--break-->

When the debugger line gets hit, type foo. Result? ReferenceError: foo is not defined. What gives? foo should be in the closure scope!

I’m guessing that Chrome is just trying to be smart here and remove variables that are never used or referenced in any function that has access to the closure scope. So, when we log foo, chrome detects that and keeps it available. When we don’t, though, it cleans it up pre-emptively.

Try this:

(function(){
    var foo = 3;
    (function(){
        debugger
        console.log(foo);
    })();
})();

Magically, foo is now defined in that inner scope.