Date.toString() is invoked first

[graduate]

Does the Date object has a special behavior when it is used in an expression?

var obj = {}, date= new Date();  20 + obj; // obj.valueOf() is called first20 + date; // date.toString() is called first, the result is a string

If I try to emulate the Date object I could not do it because in the "x + y" expressions I can't to force my object to invoke toString() method first.

[Ingolme]

You shouldn't use just the object itself. Use one of its methods or properties.