How can I use the value of the variable a as a key to lookup a property? I want to be able to say: b[whatever] and have this return 20:

var a = whatever;

var b = {a : 20};     // Want this to assign b.whatever

alert(b[whatever]); // so that this shows 20, not `undefined`

I am asking if it's possible during the creation of b, to have it contain whatever:20 instead of a:20 where whatever is itself in a variable. Maybe an eval could be used?