Difference between Null and Undefined

Null

Null is used to represent an intentional absence of value. It represents a variable whose value is undefined. It accepts only one value, which is null. The Null keyword is used to define the Null type in TypeScript, but it is not useful because we can only assign a null value to it.

Example

//Variable declared and assigned to null
var a = null; 
console.log( a );   //output: null
console.log( typeof(a) );   //output: object

Output:

Undefined

It represents uninitialized variables in TypeScript and JavaScript. It has only one value, which is undefined. The undefined keyword defines the undefined type in TypeScript, but it is not useful because we can only assign an undefined value to it.

Example

//Variable declaration without assigning any value to it
var a;      
console.log(a);  //undefined
console.log(typeof(a));  //undefined
console.log(undeclaredVar);  //Uncaught ReferenceError: undeclaredVar is not defined

Output:

Null vs. Undefined

The important difference between Null and Undefined are:

SN	Null	Undefined
1.	It is an assignment value. It can be assigned to a variable which indicates that a variable does not point any object.	It is not an assignment value. It means a variable has been declared but has not yet been assigned a value.
2.	It is an object.	It is a type itself.
3.	The null value is a primitive value which represents the null, empty, or non-existent reference.	The undefined value is a primitive value, which is used when a variable has not been assigned a value.
4.	Null indicates the absence of a value for a variable.	Undefined indicates the absence of the variable itself.
5.	Null is converted to zero (0) while performing primitive operations.	Undefined is converted to NaN while performing primitive operations.