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Undefined Vs Null in JavaScript

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In JavaScript, both undefined and null represent the absence of a meaningful value, but they are used in slightly different contexts. In this article, we are going to learn the difference between Undefined and null in JavaScript.

undefined

  • When a variable is declared but not initialized, or when a function does not return a value, the variable or the function’s result is undefined.
  • Accessing an object property or array element that does not exist also results in undefined.
  • It is a primitive value.

Example: In the example, we have shown undefined.

Javascript

let x; // variable declared but not initialized
console.log(x); // Output: undefined
 
function doSomething() {
  // no return statement, so the function returns undefined
}
console.log(doSomething()); // Output: undefined
 
let obj = {};
console.log(obj.property); // Output: undefined

                    

Output
undefined
undefined
undefined

null

  • It is a deliberate assignment that represents the absence of any object value.
  • It is often used to explicitly indicate that a variable or object property should have no value or no reference to any object.
  • It is also a primitive value.

Example: In the example, we have shown null.

Javascript

let y = null; // variable intentionally set to null
console.log(y); // Output: null
 
let obj = { property: null }; // property intentionally set to null
console.log(obj.property); // Output: null

                    

Output
null
null

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.

Difference between undefined and null

UndefinedNull
Undefined means a variable has been declared but has yet not been assigned a value.Null is an assignment value. It can be assigned to a variable as a representation of no value. 
It is an ECMAScript1 (ES1) feature.It is a Primitive value in Javascript

It does not have any syntax. But you can assign undefined to any variable but we do not do that.

Its syntax is -:

null

It is a global property.

It is not a global property.

Its supported browsers are -:

Chrome , Microsoft Edge , Internet Explorer , Firefox , Safari , Opera Mini

Its supported browsers are -:

Chrome , Microsoft Edge , Internet Explorer , Firefox , Safari , Opera Mini



Last Updated : 26 Dec, 2023
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