difference between null and undefined in javascript with example - Brave Search

What is the difference between null and undefined in JavaScript?

stackoverflow.com › questions › 5076944 › what-is-the-difference-between-null-and-undefined-in-javascript

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 undefined

null 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 object

From 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'

Answer from sebastian on Stack Overflow

stackoverflow.com › questions › 5076944 › what-is-the-difference-between-null-and-undefined-in-javascript

What is the difference between null and undefined in JavaScript? - Stack Overflow

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 undefined

null 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 object

From 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'

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.

geeksforgeeks.org › javascript › undefined-vs-null-in-javascript

Undefined Vs Null in JavaScript - GeeksforGeeks

July 23, 2025 - ... let x; // variable declared ... console.log(obj.property); // Output: undefined ... null is a special value in JavaScript that represents the deliberate absence of any object value....

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web.dev › learn › javascript › data-types › null-undefined

null and undefined | web.dev

The strict equality operator considers operands of different data types to be unequal. null == undefined > true null === undefined > false · Unlike the reserved keyword null, undefined is a property of the global object.

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 - ... In the original JavaScript implementation, undefined means a variable has been declared but has not been assigned a value. For instance, if you write: ... without assigning a value, you end up with an undefined variable.

scaler.com › topics › javascript › null-and-undefined-in-javascript

Null and Undefined in JavaScript - Scaler Topics

April 21, 2022 - Null in JavaScript means an empty value and is also a primitive type in JavaScript. The variable which has been assigned as null contains no value. Undefined, on the other hand, means the variable has been declared, but its value has not been assigned.

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.

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.

developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › null

null - JavaScript | MDN

For example, the end of the prototype chain is null because the prototype chain is composed of objects; document.querySelector() returns null if it doesn't match, because had it matched, the result would be an object. If you are designing an API, you should likely accept null and undefined ...

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syncfusion.com › blogs › post › null-vs-undefined-in-javascript

Null vs. Undefined in JavaScript | Syncfusion Blogs

December 10, 2024 - Some of the significant differences between null and undefined are: JavaScript always assigns undefined to indicate the absence of a value by default, and it never automatically assigns null as a value.

Web Dev Simplified

blog.webdevsimplified.com › 2021-01 › null-vs-undefined

Null Vs Undefined

If a variable is set to null or undefined it has no value and if a function returns null or undefined then it is saying it has no value to return. This you most likely already understand.

flexiple.com › javascript › undefined-vs-null-javascript

Undefined vs Null - Javascript - Flexiple

Let’s see what happens when you compare undefined and null using the JavaScript equality operators. // comparing undefined and null undefined == null; //true undefined === null; //false · As you can see, when the equality operator is used it compares only the values. Both undefined and null are falsy by default. So == returns true. 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.

medium.com › weekly-webtips › null-and-undefined-in-javascript-d9bc18acdaff

Null and Undefined in Javascript. What’s the difference between null and… | by Megan Lo | Webtips | Medium

February 17, 2021 - Pretty cool, right? Also I would like to point out another practical example I saw from another topic-related post. With default parameters in a function, undefined will use the default parameter while null does not.

TutorialsTeacher

tutorialsteacher.com › javascript › javascript-null-and-undefined

Difference between null and undefined in JavaScript

A null means the absence of a value. You assign a null to a variable with the intention that currently this variable does not have any value but it will have later on. It is like a placeholder for a value.

reddit.com › r/typescript › undefined vs null

r/typescript on Reddit: Undefined vs null

February 27, 2023 -

Since switching to TypeScript I have been using a lot of optional properties, for example:

type store = {
  currentUserId?: string
}

function logout () {
  store.currentUserId = undefined
}

However my coworkers and I have been discussing whether null is a more appropriate type instead of undefined, like this:

type store = {
  currentUserId: string | null
}

function logout () {
  store.currentUserId = null
}

It seems like the use of undefined in TypeScript differs slightly from in Javascript.

Do you guys/girls use undefined or null more often? And, which of the examples above do you think is better?

One reason to favor undefined over null is how javascript handle default values: const withDefault = (a = true) => { console.log(a); }; withDefault(); // logs true withDefault(undefined); // logs true withDefault(null); // logs null

They have different meanings to be: undefined means that it was never set or defined, nobody touched it. Null means someone explicitly set it to null to signal a non-value. Of course, Typescript is very permissive, you can use undefined for everything and just ditch the null, I've seen this approach used well. Or you can just use null for everything, although you may still find undefined specially if your TS settings aren't strict (they should be as strict as possible imo)

designtechworld.medium.com › what-is-the-difference-between-null-and-undefined-in-javascript-fa8ad03938a3

What is the Difference Between Null and Undefined in JavaScript? | by Sumit kumar Singh | Medium

April 4, 2023 - It is often used to assign an empty ... // null · In the above example, the variable is assigned a value of null, which indicates that it intentionally does not have any value....

naukri.com › code360 › library › difference-between-null-and-undefined-in-javascript

Difference Between Null And Undefined In Javascript

Almost there... just a few more seconds

kettanaito.com › blog › the-difference-between-null-and-undefined

The Difference Between Null and Undefined - kettanaito.com

undefined is a literal type. That's why you check typeof thing === 'undefined' to know if the type of thing is not defined at all. null is an object. If you find that wierd, the next sentence will rock your world upside down.

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.

bitskingdom.com › home › development › what’s the difference between null and undefined in javascript?

Difference Between null and undefined: A JavaScript Guide

December 16, 2024 - null signifies an explicit setting of “no value.” This is useful for resetting or clearing a variable, making your intent clear to other developers. ... undefined is the default for unassigned variables and non-existent properties, often ...

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codeburst.io › javascript-null-vs-undefined-20f955215a2

JavaScript — Null vs. Undefined. Learn the differences and similarities… | by Brandon Morelli | codeburst

January 16, 2018 - We assign the value of null to a: ... Undefined most typically means a variable has been declared, but not defined. For example: ... In JavaScript there are only six falsy values. Both null and undefined are two of the six falsy values.