It looks exactly like eval is causing the reference to be maintained.
If you change the inner function call parameter 'foo' to ('alert("hi")') you'll see the reference to foo='bar' is still maintained in the inner function. So there is no -direct- reference to foo in the inner function, but there isn't even an -indirect- reference being made in the call to eval. The reference to foo is being maintained purely because eval "might" require it. Or so it appears.
If the return eval(_var) statement is replaced with alert('blah') we're back to foo being undefined in the inner function. So I've definitely got my finger pointed at eval on this one.
If you change the inner function call parameter 'foo' to ('alert("hi")') you'll see the reference to foo='bar' is still maintained in the inner function. So there is no -direct- reference to foo in the inner function, but there isn't even an -indirect- reference being made in the call to eval. The reference to foo is being maintained purely because eval "might" require it. Or so it appears.
If the return eval(_var) statement is replaced with alert('blah') we're back to foo being undefined in the inner function. So I've definitely got my finger pointed at eval on this one.