How do I interpolate a variable as a key in a JavaScript object?

Question

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:

Answer 1

var a = "whatever";
var b = {a : 20};
b[a] = 37;
alert(b["whatever"]); // 37

'a' is a string with the value 'a'. a is a variable with the value 'whatever'.