What is the difference between null and undefined in JavaScript?

Question

I want to know what the difference is between null and undefined in JavaScript.

Answer 1

Basically, Undefined is a global variable that javascript create at the run time whether null means that no value has assigned to the variable (actually null is itself an object).

Let's take an example:

        var x;  //we declared a variable x, but no value has been assigned to it.
        document.write(x) //let's print the variable x

Undefined that's what you will get as output.

Now,

        x=5;
        y=null;
        z=x+y;

and you will get 5 as output. That's the main difference between the Undefined and null