what is the difference between null and undefined in JavaScript?

Question

Can anyone tell me what’s the difference between null and undefined in JavaScript?

Answer 1

1. Undefined is a variable which is declared but not been yet assigned a value like below:

var testVar;

alert(testVar); //shows undefined

alert(typeof testVar); //shows undefined

2. Null is variable with an assignment value to represent it contains no value:

var testVar = null;

alert(testVar); //shows null

alert(typeof testVar); //shows object

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