(function() { Array.prototype.antMethod = function() { return 'antMethod'; } console.log('--- inside closure: ' + [].antMethod()); for(var val in ['A', 'B']) { console.log('--- val in closure: '); console.log(val); } })(); console.log('--- global: ' + [].antMethod()); for(var val in ['A', 'B']) { console.log('--- val global: '); console.log(val); }