var TestVar; alert(TestVar); //shows undefined alert(typeof TestVar); //shows undefinednull is a special keyword that indicates an absence of value.
- "suresh" is string,
- true is boolean ,
- 1234 is number,
- null is undefined.
null doesn't represent a string that has no value - empty string-
Like
var a = ''; console.log(typeof a); // string console.log(a == null); //false console.log(a == undefined); // false Now if
var a; console.log(a == null); //true console.log(a == undefined); //true But
var a; console.log(a === null); //false console.log(a === undefined); // trueundefined use it to compare the variable data type
null use it to empty a value of a variable