Update
JavaScript now supports the nullish coalescing operator (??). It returns its right-hand-side operand when its left-hand-side operand is null or undefined, and otherwise returns its left-hand-side operand.
Old Answer
Please check compatibility before using it.
The JavaScript equivalent of the C# null coalescing operator (??) is using a logical OR (||):
var whatIWant = someString || "Cookies!";
There are cases (clarified below) that the behaviour won't match that of C#, but this is the general, terse way of assigning default/alternative values in JavaScript.
Clarification
Regardless of the type of the first operand, if casting it to a Boolean results in false, the assignment will use the second operand. Beware of all the cases below:
alert(Boolean(null)); // false
alert(Boolean(undefined)); // false
alert(Boolean(0)); // false
alert(Boolean("")); // false
alert(Boolean("false")); // true -- gotcha! :)
This means:
var whatIWant = null || new ShinyObject(); // is a new shiny object
var whatIWant = undefined || "well defined"; // is "well defined"
var whatIWant = 0 || 42; // is 42
var whatIWant = "" || "a million bucks"; // is "a million bucks"
var whatIWant = "false" || "no way"; // is "false"
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › Nullish_coalescing
Nullish coalescing operator (??) - JavaScript | MDN
null || undefined ?? "foo"; // raises a SyntaxError true && undefined ?? "foo"; // raises a SyntaxError · Instead, provide parenthesis to explicitly indicate precedence: ... In this example, we will provide default values but keep values other than null or undefined.
JavaScript.info
javascript.info › tutorial › the javascript language › javascript fundamentals
Nullish coalescing operator '??'
The nullish coalescing operator isn’t anything completely new. It’s just a nice syntax to get the first “defined” value of the two. We can rewrite result = a ?? b using the operators that we already know, like this: ... Now it should be absolutely clear what ?? does. Let’s see where it helps. The common use case for ?? is to provide a default value. For example, here we show user if its value isn’t null/undefined, otherwise Anonymous:
Top answer 1 of 16
2331
Update
JavaScript now supports the nullish coalescing operator (??). It returns its right-hand-side operand when its left-hand-side operand is null or undefined, and otherwise returns its left-hand-side operand.
Old Answer
Please check compatibility before using it.
The JavaScript equivalent of the C# null coalescing operator (??) is using a logical OR (||):
var whatIWant = someString || "Cookies!";
There are cases (clarified below) that the behaviour won't match that of C#, but this is the general, terse way of assigning default/alternative values in JavaScript.
Clarification
Regardless of the type of the first operand, if casting it to a Boolean results in false, the assignment will use the second operand. Beware of all the cases below:
alert(Boolean(null)); // false
alert(Boolean(undefined)); // false
alert(Boolean(0)); // false
alert(Boolean("")); // false
alert(Boolean("false")); // true -- gotcha! :)
This means:
var whatIWant = null || new ShinyObject(); // is a new shiny object
var whatIWant = undefined || "well defined"; // is "well defined"
var whatIWant = 0 || 42; // is 42
var whatIWant = "" || "a million bucks"; // is "a million bucks"
var whatIWant = "false" || "no way"; // is "false"
2 of 16
82
function coalesce() {
var len = arguments.length;
for (var i=0; i<len; i++) {
if (arguments[i] !== null && arguments[i] !== undefined) {
return arguments[i];
}
}
return null;
}
var xyz = {};
xyz.val = coalesce(null, undefined, xyz.val, 5);
// xyz.val now contains 5
this solution works like the SQL coalesce function, it accepts any number of arguments, and returns null if none of them have a value. It behaves like the C# ?? operator in the sense that "", false, and 0 are considered NOT NULL and therefore count as actual values. If you come from a .net background, this will be the most natural feeling solution.
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › Nullish_coalescing_assignment
Nullish coalescing assignment (??=) - JavaScript | MDN
No assignment is performed if the left-hand side is not nullish, due to short-circuiting of the nullish coalescing operator. For example, the following does not throw an error, despite x being const:
daily.dev
daily.dev › home › blog › webdev › nullish coalescing operator (??) in javascript - what is it and how to use it?
Nullish Coalescing Operator (??) In JavaScript - What Is It And How To Use It?
November 1, 2021 - Let us illustrate it with an example: ... In the above case, the `||` operator returns "60" because "0" is evaluated as a falsy value. In addition, `||` is a boolean logical operator, which is why it coerced "0" to a falsy value, and returned ...
GeeksforGeeks
geeksforgeeks.org › javascript › javascript-nullish-coalescing-operator
JavaScript Nullish Coalescing(??) Operator - GeeksforGeeks
Example 2: The more common use case is to set default values for JSON objects as follows. ... const foo = { bar: 0 } const valueBar = foo.bar ?? 42; const valueBaz = foo.baz ?? 42; // Value of bar: 0 console.log("Value of bar: ", valueBar); ...
Published July 12, 2025
TutorialsPoint
tutorialspoint.com › What-is-a-null-coalescing-operator-in-JavaScript
What is a "null coalescing" operator in JavaScript?
When we use the ?? operator with logical AND or OR operators, we should use the parenthesis to explicitly specify the precedence. let x = 5 || 7 ?? 9; // Syntax Error let x = (5 || 7) ?? 9; // works · In the example below, we have used nullish coalescing operator with OR operator (||) and ...
TutorialsPoint
tutorialspoint.com › javascript › javascript_nullish_coalescing_operator.htm
JavaScript - Nullish Coalescing Operator
When we use the ?? operator with logical AND or OR operators, we should use the parenthesis to explicitly specify the precedence. let x = 5 || 7 ?? 9; // Syntax Error let x = (5 || 7) ?? 9; // works · In the example below, we have used nullish coalescing operator with OR operator (||) and ...
Web Dev Simplified
blog.webdevsimplified.com › 2020-03 › javascript-null-coalesce
JavaScript Null Coalesce
It is possible to use the null coalesce operator with other logical operators like AND (&&) and OR (||), but parenthesis must be used in order to specify the order in which the logical operators evaluate. 0 || null ?? 10 // Uncaught SyntaxError: Unexpected token '??' (0 || null) ?? 10 // 10 · In the above example when no parenthesis are used an error is thrown since JavaScript is not sure what order to evaluate the operators.
W3Schools
w3schools.com › jsref › jsref_oper_nullish.asp
JavaScript Nullish Coalescing Operator
The ?? operator returns the right operand when the left operand is nullish (null or undefined), otherwise it returns the left operand. ... If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail: [email protected] · If you want to report an error, or if you want to make a suggestion, send us an e-mail: [email protected] · HTML Tutorial CSS Tutorial JavaScript Tutorial How To Tutorial SQL Tutorial Python Tutorial W3.CSS Tutorial Bootstrap Tutorial PHP Tutorial Java Tutorial C++ Tutorial jQuery Tutorial
freeCodeCamp
freecodecamp.org › news › nullish-coalescing-operator-in-javascript
How the Nullish Coalescing Operator Works in JavaScript
December 22, 2020 - So from all of the above examples, it’s clear that the result of the operation x ?? y is y only when x is either undefined or null. In all the other cases, the result of the operation will always be x. As you have seen, the nullish coalescing operator is really useful when you only care about the null or undefined value for any variable. Starting with ES6, there are many useful additions to JavaScript ...
JavaScript Tutorial
javascripttutorial.net › home › javascript tutorial › javascript nullish coalescing operator
JavaScript Nullish Coalescing Operator
October 6, 2023 - Technically, the nullish coalescing operator is equivalent to the following block: const result = value1; if(result === null || result === undefined) { result = value2; }Code language: JavaScript (javascript) A nullish value is a value that ...
Chris Pietschmann
pietschsoft.com › post › 2008 › 10 › 14 › javascript-gem-null-coalescing-using-the-or-operator
JavaScript: Null Coalesce using the || Operator | Chris Pietschmann
October 14, 2008 - Below is an example of what I used to do Previous to learning this trick: var middle = (stooge["middle-name"] != null ? stoog["middle-name"] : "(none)"); var status = (flight.status != null ? flight.status : "unknown"); This new trick makes the code much easier to read, and checks for undefined *also so I no longer need to worry about the value being equal to *undefined in some rare circumstance. JavaScript: The Good Parts by Douglas Crockford.
freeCodeCamp
freecodecamp.org › news › javascript-advanced-operators
Advanced JavaScript Operators – Nullish Coalescing, Optional Chaining, and Destructuring Assignment
January 4, 2024 - As you can see, the Nullish Coalescing Operator is a great feature that can make your code more concise and reliable. For safety reasons, the double question mark can’t be used together with JavaScript OR (||) and AND (&&) operators without parentheses () separating the operators. For example, the following code tries to see if either firstName or lastName variable can be used as the value of username before using "Guest" as its value:
OpenReplay
blog.openreplay.com › mastering-javascript-optional-chaining-and-nullish-coalescing
Mastering JavaScript: optional chaining and nullish coalescing
In this example, the age is falsy but not null or undefined, so the ?? operator will not work and will return the value of user.age. But in the case of user.address, either null or undefined, the ?? operator will return the default value Not specified. When using the Nullish Coalescing operator with objects, be careful when the default value is also an object because JavaScript objects are compared by reference, not by value.
Codecademy
codecademy.com › docs › javascript › nullish coalescing
JavaScript | Nullish Coalescing | Codecademy
January 8, 2025 - Learn how to use JavaScript — a powerful and flexible programming language for adding website interactivity. Beginner Friendly.Beginner Friendly15 hours15 hours ... The following example demonstrates the use of the nullish coalescing operator to return 18 as a default or fallback value when the variable age is null or undefined:
HackerNoon
hackernoon.com › a-nullish-coalescing-in-js-tutorial-for-normal-people
A Nullish Coalescing (in JS) Tutorial for Normal People | HackerNoon
June 24, 2023 - Nullish coalescing is a new feature that helps make that a whole lot easier. In this post, we’ll explain nullish coalescing.
freeCodeCamp
freecodecamp.org › news › what-is-the-nullish-coalescing-operator-in-javascript-and-how-is-it-useful
What is the Nullish Coalescing Operator in JavaScript, and how is it useful
May 5, 2023 - There are over four logical operators in JavaScript: the AND &&, OR ||, NOT !, and the Nullish Coalescing Operator ??.
Naresha's Blog
blog.nareshak.com › javascript-nullish-coalescing-operator
JavaScript - Nullish Coalescing Operator
February 28, 2025 - It combines two expressions to return the value of the first expression if it is neither null nor undefined or returns the value of the second expression. Let's take an example to get a clear picture. let data = null;
Fjolt
fjolt.com › article › javascript-nullish-coalescing
What is Nullish Coalescing (or ??) in Javascript
As such, using the || operator would mean that if a function returned the value 0, and we really did want to use the 0 value, we wouldn’t be able to - since 0 is falsy. With the nullish coalescing operator (??), 0 is a valid value since it only triggers if a value is null or undefined: