They are not equivalent. The first will execute the block following the if statement if myVar is truthy (i.e. evaluates to true in a conditional), while the second will execute the block if myVar is any value other than null.
The only values that are not truthy in JavaScript are the following (a.k.a. falsy values):
nullundefined0""(the empty string)falseNaN
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
Top answer 1 of 10
486
They are not equivalent. The first will execute the block following the if statement if myVar is truthy (i.e. evaluates to true in a conditional), while the second will execute the block if myVar is any value other than null.
The only values that are not truthy in JavaScript are the following (a.k.a. falsy values):
nullundefined0""(the empty string)falseNaN
2 of 10
100
Here is how you can test if a variable is not NULL:
if (myVar !== null) {...}
the block will be executed if myVar is not null.. it will be executed if myVar is undefined or false or 0 or NaN or anything else..
Videos
07:53
How to check if a value is not null and not empty string in JS ...
02:58
How to check null in Javascript using 2 ways tutorial - YouTube
Best Way to Check 'Null', 'Undefined' or 'Empty' in JavaScript ...
Is there a standard function to check for null, undefined, or blank ...
03:09
JavaScript Check null, undefined, empty, NaN & false values - YouTube
05:53
How to Check for Undefined or Null in JavaScript (2025) - YouTube
Is 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
Built In
builtin.com › software-engineering-perspectives › javascript-null-check
How to Check for Null in JavaScript | Built In
The value null is falsy, but empty objects are truthy, so typeof maybeNull === "object" && !maybeNull is an easy way to check to see that a value is not null. Finally, to check if a value has been declared and assigned a value that is neither ...
Published August 4, 2025
GeeksforGeeks
geeksforgeeks.org › javascript › how-to-check-if-a-variable-is-not-null-in-javascript
How to check if a Variable Is Not Null in JavaScript ? - GeeksforGeeks
August 5, 2025 - Example: In this example we are using typeof operator with !== undefined and !== null checks if a variable is not null in JavaScript.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › null
null - JavaScript | MDN
If you are designing an API, you should likely accept null and undefined as equivalent inputs, because many codebases have stylistic rules about when to use null or undefined by default. When checking for null or undefined, beware of the differences between equality (==) and identity (===) operators, as the former performs type-conversion. ... typeof null; // "object" (not "null" for legacy reasons) typeof undefined; // "undefined" null === undefined; // false null == undefined; // true null === null; // true null == null; // true !null; // true Number.isNaN(1 + null); // false Number.isNaN(1 + undefined); // true
Codedamn
codedamn.com › news › javascript
How to check if value is undefined or null in JavaScript
June 8, 2023 - If you want to check if a value is specifically undefined or null without type coercion, you can use the identity operator (===). The identity operator checks for both value and type equality, which means it does not perform type coercion.
Top answer 1 of 10
169
this will do the trick for you
if (!!val) {
alert("this is not null")
} else {
alert("this is null")
}
2 of 10
150
There are 3 ways to check for "not null". My recommendation is to use the Strict Not Version.
1. Strict Not Version
if (val !== null) { ... }
The Strict Not Version uses the Strict Equality Comparison Algorithm. The !== operator has faster performance than the != operator, because the Strict Equality Comparison Algorithm doesn't typecast values.
2. Non-strict Not Version
if (val != null) { ... }
The Non-strict Not Version uses the Abstract Equality Comparison Algorithm. The != operator has slower performance than the !== operator, because the Abstract Equality Comparison Algorithm typecasts values.
3. Double Not Version
if (!!val) { ... }
The Double Not Version has faster performance than both the Strict Not Version and the Non-Strict Not Version. However, the !! operator will typecast "falsey" values like 0, '', undefined and NaN into false, which may lead to unexpected results, and it has worse readability because null isn't explicitly stated.
freeCodeCamp
freecodecamp.org › news › how-to-check-for-null-in-javascript
JS Check for Null – Null Checking in JavaScript Explained
November 7, 2024 - But, this can be tricky because if the variable is undefined, it will also return true because both null and undefined are loosely equal. let firstName = null; let lastName; console.log(firstName == null); // true console.log(lastName == null); // true console.log(firstName == undefined); // true console.log(lastName == undefined); // true console.log(firstName == lastName); // true console.log(null == undefined); // true · Note: This can be useful when you want to check if a variable has no value because when a variable has no value, it can either be null or undefined.
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.
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
The isEmpty function uses the equality operator (==) to check if the argument value is null or undefined. This works because if one of the operands is null or undefined, the other operand must be null or undefined for the equality comparison ...
DEV Community
dev.to › wolfhoundjesse › null-checking-in-javascript-lc4
Null-checking in JavaScript - DEV Community
April 11, 2019 - What are your thoughts? How are you checking for empty or null values? Bonus if you comment with examples in other programming languages! ... It's more a bright exemple of how to make simple things looks complicated because in javascript if(tokenInfo) will check if variable is either :
Bobby Hadz
bobbyhadz.com › blog › javascript-check-if-variable-is-not-null
Check if a Variable is Not NULL in JavaScript | bobbyhadz
Copied!const a = 'hello'; if (a) { console.log(`🚨 a is NOT false, 0, empty string, null, undefined, NaN`); } else { console.log(`⛔️️ a is ONE OF false, 0, empty string, null, undefined, NaN`); } In this example, we check if the value stored in the variable a is truthy. Truthy are all values that are not falsy. The falsy values in JavaScript are: false, 0, "", null, undefined, NaN.
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 › check-if-string-is-empty-or-null-javascript
How to Check if a String is Empty or Null in JavaScript – JS Tutorial
November 7, 2024 - In this example, we're first using the trim method to remove any leading or trailing whitespace characters from the str variable, then checking whether the resulting string has zero length. If it does, then we know that the string is empty. Otherwise, we know that the string is not empty. Here are some best practices to follow when checking for empty or null strings in JavaScript:
TutorialsPoint
tutorialspoint.com › how-do-i-check-for-null-values-in-javascript
How do I check for null values in JavaScript?
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.
GeeksforGeeks
geeksforgeeks.org › javascript › how-to-check-for-null-values-in-javascript
How to check for null values in JavaScript ? - GeeksforGeeks
July 23, 2025 - Lodash _.isNull() method is used to find whether the value of the object is null. If the value is null then returns true otherwise it returns false. ... Example: In this example, we are checking whether the given value is null or not by the ...
Futurestud.io
futurestud.io › tutorials › check-if-a-value-is-null-or-undefined-in-javascript-or-node-js
Check if a Value Is Null or Undefined in JavaScript or Node.js
I’m the maintainer of the @supercharge/goodies package providing convenient helper functions for Node.js and JavaScript. This package comes with a handy isNullish(value) method determining whether the given value is null or undefined: const { isNullish } = require('@supercharge/goodies') isNullish(null) // true isNullish(undefined) // true isNullish(0) // false isNullish('') // false isNullish({}) // false isNullish([]) // false isNullish(false) // false · Notice: the isNullish method is fully typed and your code editor or IDE knows that the provided value is either null/undefined or not.
Javatpoint
javatpoint.com › how-to-check-if-a-variable-is-not-null-in-javascript
How to check if a variable is not NULL in JavaScript - javatpoint
How to check if a variable is not NULL in JavaScript with javascript tutorial, introduction, javascript oops, application of javascript, loop, variable, objects, map, typedarray etc.
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
In simple words you can say a null ... if a variable is undefined or null you can use the equality operator == or strict equality operator === (also called identity operator)....
Top answer 1 of 11
226
If you truly want to confirm that a variable is not null and not an empty string specifically, you would write:
if(data !== null && data !== '') {
// do something
}
Notice that I changed your code to check for type equality (!==|===).
If, however you just want to make sure, that a code will run only for "reasonable" values, then you can, as others have stated already, write:
if (data) {
// do something
}
Since, in javascript, both null values, and empty strings, equals to false (i.e. null == false).
The difference between those 2 parts of code is that, for the first one, every value that is not specifically null or an empty string, will enter the if. But, on the second one, every true-ish value will enter the if: false, 0, null, undefined and empty strings, would not.
2 of 11
28
Instead of using
if(data !== null && data !== '' && data!==undefined) {
// do something
}
You can use below simple code
if(Boolean(value)){
// do something
}
- Values that are intuitively “empty”, like 0, an empty string, null, undefined, and NaN, become false
- Other values become true