How can a JavaScript object refer to values in itself? [duplicate]

Lets say I have the following JavaScript:

var obj = {
 key1 : "it ",
 key2 : key1 + " works!"
};
alert(obj.key2);

This errors with “key1 is not defined”. I have tried

this.key1
this[key1]
obj.key1
obj[key1]
this["key1"]
obj["key1"]

and they never seem to be defined.

How can I get key2 to refer to key1’s value?