Is null an object? [duplicate]

Question

Possible Duplicate:
Null object in javascript

Null is an object right? So if i set x to null, why can't i get the constructor value?

 var x = null;
 alert(typeof x);
 alert(x.constructor);

Answer 1

null in JS is a primitive value. It wasn't constructed by any constructor function, so it doesn't have a constructor property. typeof null being 'object' is basically a horrible lie retained for historical reasons. Don't expect too much consistency from JS, you'll be disappointed!

Primitive values can often behave like objects in JS due to autoboxing: (1).constructor works despite 1 also being a primitive value, because it implicitly calls new Number(1). But there is no Object form of null (or undefined) to automatically convert to, so in this case you get an error.

In general you should avoid using constructor. For many class/instance models built on top of JS it doesn't do what you think at all. instanceof typically works better.