Does comparison to 'undefined` still does a global scope lookup?

Question

Accordigng to http://www.ecma-international.org/ecma-262/5.1/#sec-15.1.1.3 undefined can't no longer be redefined.

Does it imply that global lookup (to find if undefined was redefined) is not happening anymore?

Though, it does seem to be unnecessary now :)

UPDATE Of course the question is about the strict mode :) Thanks T.J.

Answer 1

If you're not in the global scope, you still have to do a lookup for a local undefined variable (which could be 1, null, 'fjakfjadjfjlfjsdkj', or any other random thing), since undefined is not a reserved word. Otherwise though, a browser that supports ES5 could do so in theory, as the global undefined variable could never be changed.