JavaScript is very flexible with regards to checking for "null" values. I'm guessing you're actually looking for empty strings, in which case this simpler code will work:
if(!pass || !cpass || !email || !cemail || !user){
Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN.
Please note that if you are specifically checking for numbers, it is a common mistake to miss 0 with this method, and num !== 0 is preferred (or num !== -1 or ~num (hacky code that also checks against -1)) for functions that return -1, e.g. indexOf).
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › null
null - JavaScript - MDN Web Docs
Unlike undefined, JSON.stringify() can represent null faithfully. JavaScript is unique to have two nullish values: null and undefined. Semantically, their difference is very minor: undefined represents the absence of a value, while null represents the absence of an object.
Top answer 1 of 16
1093
JavaScript is very flexible with regards to checking for "null" values. I'm guessing you're actually looking for empty strings, in which case this simpler code will work:
if(!pass || !cpass || !email || !cemail || !user){
Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN.
Please note that if you are specifically checking for numbers, it is a common mistake to miss 0 with this method, and num !== 0 is preferred (or num !== -1 or ~num (hacky code that also checks against -1)) for functions that return -1, e.g. indexOf).
2 of 16
732
To check for null SPECIFICALLY you would use this:
if (variable === null)
This test will ONLY pass for null and will not pass for "", undefined, false, 0, or NaN.
Additionally, I've provided absolute checks for each "false-like" value (one that would return true for !variable).
Note, for some of the absolute checks, you will need to implement use of the absolutely equals: === and typeof.
I've created a JSFiddle here to show all of the individual tests working
Here is the output of each check:
Null Test:
if (variable === null)
- variable = ""; (false) typeof variable = string
- variable = null; (true) typeof variable = object
- variable = undefined; (false) typeof variable = undefined
- variable = false; (false) typeof variable = boolean
- variable = 0; (false) typeof variable = number
- variable = NaN; (false) typeof variable = number
Empty String Test:
if (variable === '')
- variable = ''; (true) typeof variable = string
- variable = null; (false) typeof variable = object
- variable = undefined; (false) typeof variable = undefined
- variable = false; (false) typeof variable = boolean
- variable = 0; (false) typeof variable = number
- variable = NaN; (false) typeof variable = number
Undefined Test:
if (typeof variable == "undefined")
-- or --
if (variable === undefined)
- variable = ''; (false) typeof variable = string
- variable = null; (false) typeof variable = object
- variable = undefined; (true) typeof variable = undefined
- variable = false; (false) typeof variable = boolean
- variable = 0; (false) typeof variable = number
- variable = NaN; (false) typeof variable = number
False Test:
if (variable === false)
- variable = ''; (false) typeof variable = string
- variable = null; (false) typeof variable = object
- variable = undefined; (false) typeof variable = undefined
- variable = false; (true) typeof variable = boolean
- variable = 0; (false) typeof variable = number
- variable = NaN; (false) typeof variable = number
Zero Test:
if (variable === 0)
- variable = ''; (false) typeof variable = string
- variable = null; (false) typeof variable = object
- variable = undefined; (false) typeof variable = undefined
- variable = false; (false) typeof variable = boolean
- variable = 0; (true) typeof variable = number
- variable = NaN; (false) typeof variable = number
NaN Test:
if (typeof variable == 'number' && !parseFloat(variable) && variable !== 0)
-- or --
if (isNaN(variable))
- variable = ''; (false) typeof variable = string
- variable = null; (false) typeof variable = object
- variable = undefined; (false) typeof variable = undefined
- variable = false; (false) typeof variable = boolean
- variable = 0; (false) typeof variable = number
- variable = NaN; (true) typeof variable = number
As you can see, it's a little more difficult to test against NaN;
Videos
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GeeksforGeeks
geeksforgeeks.org › javascript › null-in-javascript
Null in JavaScript - GeeksforGeeks
June 5, 2024 - In JavaScript, `null` indicates the deliberate absence of any object value. It's a primitive value that denotes the absence of a value or serves as a placeholder for an object that isn't present.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Global_Objects › null
null - JavaScript | MDN
May 23, 2022 - The null keyword refers to the null primitive value, which represents the intentional absence of any object value.
web.dev
web.dev › learn › javascript › data-types › null-undefined
null and undefined | web.dev
The null keyword represents an intentionally defined absence of value. null is a primitive, although the typeof operator returns that null is an object. This is an error that has carried over from the first version of JavaScript and been left ...
freeCodeCamp
freecodecamp.org › news › how-to-check-for-null-in-javascript
JS Check for Null – Null Checking in JavaScript Explained
November 7, 2024 - Null is a primitive type in JavaScript. This means you are supposed to be able to check if a variable is null with the typeof() method. But unfortunately, this returns “object” because of an historical bug that cannot be fixed. let userName ...
Built In
builtin.com › software-engineering-perspectives › javascript-null-check
How to Check for Null in JavaScript | Built In
Summary: JavaScript offers several ways to check for null, including strict (===) and loose (==) equality, Object.is() and boolean coercion. Developers often use typeof and optional chaining (?.) to safely identify null, undefined or undeclared ...
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.
CoreUI
coreui.io › answers › how-to-check-if-a-variable-is-null-in-javascript
How to check if a variable is null in JavaScript · CoreUI
November 6, 2025 - Here value === null uses strict equality to check if the variable is exactly null. This approach distinguishes null from other falsy values like undefined, 0, false, or empty strings. Unlike loose equality == null which also matches undefined, strict equality ensures you’re checking for null specifically.
JavaScript Tutorial
javascripttutorial.net › home › an essential guide to javascript null
An Essential Guide to JavaScript null
September 29, 2020 - JavaScript uses the null value to represent the intentional absence of any object value.
DEV Community
dev.to › wolfhoundjesse › null-checking-in-javascript-lc4
Null-checking in JavaScript - DEV Community
April 11, 2019 - Cofounded Host Collective (DiscountASP.net). Cofounded Player Axis (Social Gaming). Computer Scientist and Technology Evangelist with 20+ years of experience with JavaScript! ... Looking at this block of code... if ( tokenInfo && tokenInfo !== undefined && tokenInfo !== null && tokenInfo !== "" ) { }
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.
Syncfusion
syncfusion.com › blogs › javascript › null vs. undefined in javascript
Null vs. Undefined in JavaScript | Syncfusion Blogs
December 10, 2024 - The primitive type null indicates the intentional absence of a value. Therefore, in JavaScript, programmers often assign null to a variable to denote that the variable is declared and initialized and currently doesn’t hold a value.
Dmitri Pavlutin
dmitripavlutin.com › javascript-null
Everything about null in JavaScript - Dmitri Pavlutin
September 21, 2020 - null in JavaScript is a special value that represents a missing object.
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 - When a javascript object is being serialized, all undefined properties are discarded, remember 'undefined' means a property is yet to be assigned a value. But null on the other hand is known by JSON as its a valid JSON data type
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › Nullish_coalescing
Nullish coalescing operator (??) - JavaScript - MDN Web Docs
The nullish coalescing (??) operator is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.
GeeksforGeeks
geeksforgeeks.org › javascript › how-to-check-for-null-values-in-javascript
How to check for null values in JavaScript ? - GeeksforGeeks
July 23, 2025 - The null values show the non-appearance of any object value. It is usually set on purpose to indicate that a variable has been declared but not yet assigned any value. This contrasts null from the similar primitive value undefined, which is ...
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 ...
Medium
medium.com › javascript-scene › handling-null-and-undefined-in-javascript-1500c65d51ae
Handling null and undefined in JavaScript | by Eric Elliott | JavaScript Scene | Medium
November 12, 2019 - In other words, Arrays in JavaScript can fill the role of Maybes from languages like Haskell. A Maybe is a special abstract data type that encapsulates an optional value. The data type takes two forms: ... const log = x => console.log(x); const exists = x => x != null;const Just = value => ({ map: f => Just(f(value)), });const Nothing = () => ({ map: () => Nothing(), });const Maybe = value => exists(value) ?
Mastering JS
masteringjs.io › tutorials › fundamentals › null
`null` in JavaScript - Mastering JS
December 2, 2020 - In JavaScript, null is a value that represents the intentional absence of any object value. It is technically a primitive type, although in some cases it behaves as an object.