Undefined Vs Null in JavaScript

There are several differences between null and undefined, which are sometimes understood as the same.

Definition:

Null: It is the intentional absence of the value. It is one of the primitive values of JavaScript.

Undefined: It means the value does not exist in the compiler. It is the global object.

Type:

Null: Object 

Undefined: undefined

You can see refer to “==” vs “===” article.

 
 null == undefined // true
 null === undefined // false

It means null is equal to undefined but not identical.

When we define a variable to undefined then we are trying to convey that the variable does not exist . When we define a variable to null then we are trying to convey that the variable is empty.

Differentiating using isNaN(): You can refer to NaN article for better understanding.

isNaN(2 +  null)      // false
isNaN(2 + undefined) // true

Examples:

Null:

null ? console.log("true") : console.log("false") // false

Null is also referred as false.

Undefined:

When variable is not assigned a value

var temp;
if(temp === undefined)
console.log("true");
else
console.log("false");

• Output:

 true

Accessing values which does not exist

var temp=['a','b','c'];
if(temp[3] === undefined)
console.log("true");
else
console.log("false");

• Output:

true

Let us see the differences in a tabular form -:

	Undefined	NULL
1.	The undefined property indicates that a variable has not been declared at all.	The value null represents the absence of any object value
2.	It is an ECMAScript1 (ES1) feature.	It is Primitive value in Javascript
3.	Its supported browsers are -: Chrome , Microsoft Edge , Internet Explorer , Firefox , Safari , Opera Mini	Its syntax is -: null
4.	It is a global property.	Its supported browsers are -: Chrome , Microsoft Edge , Internet Explorer , Firefox , Safari , Opera Mini

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