You can use the qualities of the abstract equality operator to do this:
if (variable == null){
// your code here.
}
Because null == undefined is true, the above code will catch both null and undefined.
Top answer 1 of 16
3579
You can use the qualities of the abstract equality operator to do this:
if (variable == null){
// your code here.
}
Because null == undefined is true, the above code will catch both null and undefined.
2 of 16
1403
The standard way to catch null and undefined simultaneously is this:
if (variable == null) {
// do something
}
--which is 100% equivalent to the more explicit but less concise:
if (variable === undefined || variable === null) {
// do something
}
When writing professional JS, it's taken for granted that type equality and the behavior of == vs === is understood. Therefore we use == and only compare to null.
Edit again
The comments suggesting the use of typeof are simply wrong. Yes, my solution above will cause a ReferenceError if the variable doesn't exist. This is a good thing. This ReferenceError is desirable: it will help you find your mistakes and fix them before you ship your code, just like compiler errors would in other languages. Use try/catch if you are working with input you don't have control over.
You should not have any references to undeclared variables in your code.
freeCodeCamp
freecodecamp.org › news › how-to-check-for-null-in-javascript
JS Check for Null – Null Checking in JavaScript Explained
November 7, 2024 - This article will teach you how to check for null, along with the difference between the JavaScript type null and undefined. Null and undefined are very similar in JavaScript and are both primitive types. A variable has the type of null if it intentionally contains the value of null. In contrast, a variable has the type of undefined when you declare it without initiating a value. // This is null let firstName = null; // This is undefined let lastName;
Good way to check for variable being not null and not undefined.
There are some style guides that basically say you always should use ===, but you can use == in order to check for null or undefined at the same time. So you could do the following: if (value != null) { // This will run if `value` is not `null` and not `undefined`. } More on reddit.com
56
32
October 20, 2016What is the best method to check if a variable is not null or empty?
It depends what you mean by empty, or how strict you want to be. These values will coerce to false: undefined null '' (empty string) 0 NaN Everything else coerces to true. So, if you are OK with rejecting all of those values, you can do: if(PostCodeInformation) { } If you want to make sure that PostCodeInformation is really an object value (and not a number or boolean, etc): if(typeof PostCodeInformation === 'object' && PostCodeInformation !== null) { } You have to do the null-check there, because in JavaScript typeof null returns 'object'. So dumb. If you want to make sure that PostCodeInformation has some property that you really need: if(PostCodeInformation && PostCodeInformation.myCoolProperty) { } Etc, etc More on reddit.com
18
3
August 2, 2015Is null false in JavaScript?
Null is not considered false in JavaScript, but it is considered falsy. This means that null is treated as if it’s false when viewed through boolean logic. However, this is not the same thing as saying null is false or untrue.
builtin.com
builtin.com › software-engineering-perspectives › javascript-null-check
How to Check for Null in JavaScript | Built In
What is a null check?
In JavaScript, null represents an intentional absence of a value, indicating that a variable has been declared with a null value on purpose. On the other hand, undefined represents the absence of any object value that is unintentional. A null check determines whether a variable has a null value, meaning a valid instance of a type exists.
builtin.com
builtin.com › software-engineering-perspectives › javascript-null-check
How to Check for Null in JavaScript | Built In
What is a strict null check?
StrictNullChecks is a feature that treats null and undefined as two separate types, reducing errors and making it easier to find coding bugs. It also has stronger measures for defining variables as null or undefined, ensuring variables are declared as null only when it’s safe to do so.
builtin.com
builtin.com › software-engineering-perspectives › javascript-null-check
How to Check for Null in JavaScript | Built In
Videos
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How to check null in Javascript using 2 ways tutorial - YouTube
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JavaScript Check null, undefined, empty, NaN & false values - YouTube
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How to Check if Variable is Undefined or Null in Javascript - YouTube
Built In
builtin.com › software-engineering-perspectives › javascript-null-check
How to Check for Null in JavaScript | Built In
So, when programming to check if a variable has any value at all before trying to process it, you can use == null to check for either null or undefined. Some JavaScript programmers prefer everything to be explicit, and there is nothing wrong ...
Published August 4, 2025
Reddit
reddit.com › r/javascript › good way to check for variable being not null and not undefined.
r/javascript on Reddit: Good way to check for variable being not null and not undefined.
October 20, 2016 -
Hi, all, I often do stuff like this in my code, to check for a variable being not null and not undefined.
// check if value is not null and not undefined
if (value) {
...
}However, I'm now thinking this can leads to bugs, because of 0, "", false and NaN also being falsy.
What is a better way to check a variable is not null and not undefined? I could use this I think, wondering if there is something shorter than this:
if (typeof value !== 'undefined' || value !== null) {
...
} Top answer 1 of 5
29
There are some style guides that basically say you always should use ===, but you can use == in order to check for null or undefined at the same time. So you could do the following: if (value != null) { // This will run if `value` is not `null` and not `undefined`. }
2 of 5
18
fyi your if statement doesn't match your description of it: What is a better way to check a variable is not null and not undefined? what you have now checks if it's not null or not undefined, which will always pass the check and enter the body of the if statement. you want something like: if (typeof value !== 'undefined' && value !== null) { ... } But honestly, the majority of the time if (value) { ... } is exactly what you want, and is well understood and idiomatic
GeeksforGeeks
geeksforgeeks.org › javascript › how-to-check-for-null-undefined-or-blank-variables-in-javascript
How to check for null, undefined or blank Variables in JavaScript ? - GeeksforGeeks
May 7, 2023 - One of the most common is to use the triple equals (===) operator, which checks for both value and type equality. ... Undefined: A variable that is undefined has not been assigned a value.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › null
null - JavaScript | MDN
October 28, 2025 - function getVowels(str) { const m = str.match(/[aeiou]/gi); if (m === null) { return 0; } return m.length; } console.log(getVowels("sky")); // Expected output: 0 ... The keyword null is a literal for the null value. Unlike undefined, which is a global variable, null is not an identifier but ...
Codedamn
codedamn.com › news › javascript
How to check if value is undefined or null in JavaScript
June 8, 2023 - For example: let myVar = null; ... The easiest way to check if a value is either undefined or null is by using the equality operator (==)....
Stack Abuse
stackabuse.com › javascript-check-if-variable-is-a-undefined-or-null
JavaScript: Check if Variable is undefined or null
March 29, 2023 - In this short guide, we've taken a look at how to check if a variable is null, undefined or nil in JavaScript, using the ==, === and typeof operators, noting the pros and cons of each approach.
GeeksforGeeks
geeksforgeeks.org › javascript › how-to-check-for-null-values-in-javascript
How to check for null values in JavaScript ? - GeeksforGeeks
July 23, 2025 - Checking undeclared variable: true ... null nor undefined: true false is neither null nor undefined: true · Lodash _.isNull() method is used to find whether the value of the object is null....
LogRocket
blog.logrocket.com › home › how to check for null, undefined, or empty values in javascript
How to check for null, undefined, or empty values in JavaScript - LogRocket Blog
February 14, 2025 - Learn how to write a null check function in JavaScript and explore the differences between the null and undefined attributes.
freeCodeCamp
freecodecamp.org › news › javascript-nullable-how-to-check-for-null-in-js
JavaScript Nullable – How to Check for Null in JS
July 7, 2022 - Object.is(<null_variable>,null) is an equally reliable way to check for null. Take heart! As you've probably gathered, there are a plethora of brain teasers in the JavaScript ecosystem like this.
Programiz
programiz.com › javascript › examples › check-undefined-null
JavaScript Program To Check If A Variable Is undefined or null
... // program to check if a variable is undefined or null function checkVariable(variable) { if( typeof variable === 'undefined' || variable === null ) { console.log('The variable is undefined or null'); } else { console.log('The variable is neither undefined nor null'); } } let newVariable; ...
DEV Community
dev.to › wolfhoundjesse › null-checking-in-javascript-lc4
Null-checking in JavaScript - DEV Community
April 11, 2019 - Then I can use the classic if (tokenInfo) for actual boolean checks only and avoid having to remember whether it is a boolean check or a truthy/falsy check. ... Polyglot, autodidact. OSS author and contributor. Addicted to writing code, seeking my next 'fix'. Love communicating with an audience whose eyes don't glaze over when I get to the 'good parts'. ... Never use null unless you're trying to express an actual null value. Checking for !variable is usually a sufficient check for undefined unless the variable is boolean.
Favtutor
favtutor.com › articles › null-javascript
Check for Null in JavaScript | 3 Easy Methods (with code)
January 5, 2024 - In this example, we use the typeof operator to check if the type of variable is an Object and it holds a null value. If both conditions are satisfied, then the variable holds a null value.
TutorialsPoint
tutorialspoint.com › How-do-I-check-for-null-values-in-JavaScript
How do I check for null values in JavaScript?
July 22, 2022 - The typeof operator may be used to determine the data type of a JavaScript variable. Here we use the typeof operator with the null operator. The (!variable) means the value is not null and if it is checked with the typeof operator variable which has the data type of an object then the value is null.
freeCodeCamp
forum.freecodecamp.org › javascript
Undefined vs null - JavaScript - The freeCodeCamp Forum
November 19, 2019 - Hello. What is the difference between undefined and null?
TutorialsPoint
tutorialspoint.com › how-to-check-for-null-undefined-or-blank-variables-in-javascript
How to check for null, undefined, or blank variables in JavaScript?
August 8, 2022 - So, we can check that if the variable contains the null value or undefined value, it means we have a null variable. if (variable == null || variable === 'undefined') { // variable is undefined or null }
Reddit
reddit.com › r/javascript › what is the best method to check if a variable is not null or empty?
r/javascript on Reddit: What is the best method to check if a variable is not null or empty?
August 2, 2015 -
I've seen so many methods; but I am looking for a simple style I can adopt in my code to keep it consistent:
if (PostCodeInformation !== null PostCodeInformation !== undefined){
}
Top answer 1 of 5
9
It depends what you mean by empty, or how strict you want to be. These values will coerce to false: undefined null '' (empty string) 0 NaN Everything else coerces to true. So, if you are OK with rejecting all of those values, you can do: if(PostCodeInformation) { } If you want to make sure that PostCodeInformation is really an object value (and not a number or boolean, etc): if(typeof PostCodeInformation === 'object' && PostCodeInformation !== null) { } You have to do the null-check there, because in JavaScript typeof null returns 'object'. So dumb. If you want to make sure that PostCodeInformation has some property that you really need: if(PostCodeInformation && PostCodeInformation.myCoolProperty) { } Etc, etc
2 of 5
5
What you want is val != null. With coersion this will only be true if val is not null or undefined.
Sentry
sentry.io › sentry answers › javascript › how do i check for an empty/undefined/null string in javascript?
How do I Check for an Empty/Undefined/Null String in JavaScript? | Sentry
This works because if one of the operands is null or undefined, the other operand must be null or undefined for the equality comparison to return true. If the argument value is not null or undefined, the right side of the logical OR (||) operator is evaluated. To check for an empty string, the logical && operator is used.
Scaler
scaler.com › topics › javascript-check-null
JavaScript Program to Check for Null - Scaler Topics
May 4, 2023 - In the first step, we created a variable x and initialized it with a null value. Inside the if condition, we are simply checking the value of x is null or not by using the equality operator '=='