For beginners, sometimes an easy thing is the hardest thing to look for in tutorials/documentation. They’re just too simple that most documentation will not cover it, or searching on google will give you bunch of rubbish results…
Anyway, I’ll cut the crap, here’s my question 
How to check if a key/value pair exists in associate array (Object) in AS3? In PHP you can do something like
if (isset($foo[‘bar’])) echo “exist”;
