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

Both Null and undefined in JavaScript indicate absence of value.

var a = null; //variable assigned null value
var b;  // undefined

Despite the fact both exist for absence of value but: Undefined actually means the variable is not initialized. Functions that return nothing and function parameters for which no value is supplied, undefined value is returned. Use strict equality operator === to distinguish between null and undefined.

Reference: http://www.thesstech.com/javascript/null-and-undefined