undefined means a variable has been declared but has not yet been assigned a value :
var testVar;
console.log(testVar); //shows undefined
console.log(typeof testVar); //shows undefinednull is an assignment value. It can be assigned to a variable as a representation of no value :
var testVar = null;
console.log(testVar); //shows null
console.log(typeof testVar); //shows objectFrom the preceding examples, it is clear that undefined and null are two distinct types: undefined is a type itself (undefined) while null is an object.
Proof :
console.log(null === undefined) // false (not the same type)
console.log(null == undefined) // true (but the "same value")
console.log(null === null) // true (both type and value are the same)and
null = 'value' // Uncaught SyntaxError: invalid assignment left-hand side
undefined = 'value' // 'value'
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › null
null - JavaScript | MDN
The keyword null is a literal for the null value. Unlike undefined, which is a global variable, null is not an identifier but a syntax keyword.
W3docs
w3docs.com › javascript
The Difference Between Null and Undefined in JavaScript
console.log(typeof null); // "object" ... console.log(!null ); // true ... To sum up, in JavaScript null means "nothing" and “empty”, something that does not exist....
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web.dev
web.dev › learn › javascript › data-types › null-undefined
null and undefined | web.dev
Learn how to use JavaScript's `null` and `undefined` data types.
Top answer 1 of 16
1651
undefined means a variable has been declared but has not yet been assigned a value :
var testVar;
console.log(testVar); //shows undefined
console.log(typeof testVar); //shows undefinednull is an assignment value. It can be assigned to a variable as a representation of no value :
var testVar = null;
console.log(testVar); //shows null
console.log(typeof testVar); //shows objectFrom the preceding examples, it is clear that undefined and null are two distinct types: undefined is a type itself (undefined) while null is an object.
Proof :
console.log(null === undefined) // false (not the same type)
console.log(null == undefined) // true (but the "same value")
console.log(null === null) // true (both type and value are the same)and
null = 'value' // Uncaught SyntaxError: invalid assignment left-hand side
undefined = 'value' // 'value'
2 of 16
803
The difference can be explained with toilet tissue holder:
A non-zero value is like a holder with roll of toilet tissue and there's tissue still on the tube.
A zero value is like a holder with an empty toilet tissue tube.
A null value is like a holder that doesn't even have a tissue tube.
An undefined value is similar to the holder itself being missing.
W3Schools Blog
w3schools.blog › home › difference between undefined value and null value
Difference between undefined value and null value - W3schools
April 24, 2018 - Undefined value: A value that is not defined and has no keyword is known as an undefined value. ... Note: Undefined is of the type undefined. var testNum; console.log(typeof testNum); // undefined · Null value: A value that is explicitly specified by the keyword “null” is known as a null value.
SheCodes
shecodes.io › athena › 2227-what-is-the-difference-between-null-and-undefined-in-javascript
[JavaScript] - What is the Difference Between Null and Undefined in JavaScript?
Learn what is the difference between null and undefined in JavaScript and how to distinguish between them. Check how to use a typeof operator.
W3Schools
w3schools.com › js › js_typeof.asp
JavaScript typeof
Unfortunately, in JavaScript, the data type of null is an object. ... // Create an Object let person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}; person = null; // Now value is null, but type is still an object Try it Yourself » · You can also empty an object by setting it to undefined: let person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"}; person = undefined; // Now both value and type is undefined Try it Yourself »
TutorialsPoint
tutorialspoint.com › What-is-the-difference-between-null-and-undefined-in-JavaScript
What is the difference between null and undefined in JavaScript?
In JavaScript, use null to explicitly indicate that a variable has no value or is intentionally empty. Use undefined when something is naturally missing, such as an uninitialized variable or a non-existing object property.
Scaler
scaler.com › topics › javascript › null-and-undefined-in-javascript
Null and Undefined in JavaScript - Scaler Topics
April 21, 2022 - The setting of the value must be done manually by the user as JavaScript never sets the value as null. An object can be emptied by setting it to null. ... Here we have assigned the value null to variable x. There is a subtle difference between null and undefined, but as a programmer, it is important that we understand it clearly.
TutorialsTeacher
tutorialsteacher.com › javascript › javascript-null-and-undefined
Difference between null and undefined in JavaScript
The type of null variable is object whereas the type of undefined variable is "undefined".
GeeksforGeeks
geeksforgeeks.org › javascript › undefined-vs-null-in-javascript
Undefined Vs Null in JavaScript - GeeksforGeeks
July 23, 2025 - undefined indicates a variable hasn’t been initialized, while null is intentionally assigned to indicate no value. Understanding the distinction helps write cleaner, more predictable code in JavaScript, especially when handling default values or checking for missing data. ... Help us improve. Share your suggestions to enhance the article. Contribute your expertise and make a difference in the GeeksforGeeks portal.
Tutorial Republic
tutorialrepublic.com › faq › how-to-determine-if-variable-is-undefined-or-null-in-javascript.php
How to Determine If Variable is Undefined or NULL in JavaScript
<script> var firstName; var lastName = null; // Try to get non existing DOM element var comment = document.getElementById('comment'); console.log(firstName); // Print: undefined console.log(lastName); // Print: null console.log(comment); // Print: null console.log(typeof firstName); // Print: undefined console.log(typeof lastName); // Print: object console.log(typeof comment); // Print: object console.log(null == undefined) // Print: true console.log(null === undefined) // Print: false /* Since null == undefined is true, the following statements will catch both null and undefined */ if(firstNa
Programiz
programiz.com › javascript › null-undefined
JavaScript null and undefined
When comparing null and undefined with equal to operator ==, they are considered equal. For example, ... In JavaScript, == compares values by performing type conversion. Both null and undefined return false.
W3Schools
w3schools.com › typescript › typescript_null.php
TypeScript Null & Undefined
null and undefined are primitive types and can be used like other types, such as string. let value: string | undefined | null = null; value = 'hello'; value = undefined; Try it Yourself » · When strictNullChecks is enabled, TypeScript requires ...
W3Schools
w3schools.com › js › tryit.asp
W3Schools online HTML editor
The W3Schools online code editor allows you to edit code and view the result in your browser
W3Schools
w3schools.com › jsref › jsref_undefined.asp
JavaScript undefined Property
The undefined property indicates that a variable has not been assigned a value, or not declared at all. undefined() is an ECMAScript1 (JavaScript 1997) feature.
DEV Community
dev.to › sduduzog › null-vs-undefined-what-to-choose-what-to-use-11g
null vs undefined? What to choose? What to use? - DEV Community
August 23, 2023 - "But black dynamite, assigning null to a variable does the same thing" see that's where you'd be wrong. Here's an analogy for you. We can say null is like loading a webpage and just getting a blank screen, but undefined is a '404 not found' error.
Flexiple
flexiple.com › javascript › undefined-vs-null-javascript
Undefined vs Null - Javascript - Flexiple
But when we use the strict equality operator (===) which checks both type and value, since undefined and null are of different types (from the typeof Operator section), the strict equality operator returns false. As promised, now let’s look as to why the type of null is an “object”. As it then indicates that null must be an object, which is not true. In fact, null is one of the primitive values in JavaScript.
Medium
medium.com › weekly-webtips › null-and-undefined-in-javascript-d9bc18acdaff
Null and Undefined in Javascript
February 17, 2021 - Quick Note: As mentioned earlier, null and undefined are both primitive values, but interestingly enough, if we test out in typeof , they gave us different result: All other values in Javascript are objects ({}, [], functions…). So, this is ...
CoreUI
coreui.io › blog › what-is-the-difference-between-null-and-undefined-in-javascript
What is the Difference Between Null and Undefined in JavaScript · CoreUI
February 9, 2025 - This article will walk you through ... them. ... In the original JavaScript implementation, undefined means a variable has been declared but has not been assigned a value....