Javascript Introduction
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Javascript Variables
Difference between var, let and const in Javascript
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Nullish coalescing operator in Javascript
Break and Continue in Javascript
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Javascript Objects

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Javascript Error Handling
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Javascript ES6
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Javascript Design Principles
SOLID - The Single responsibility principle in javascript
SOLID - Open-Closed principle in Javascript

Other Topics
Javascript Hoisting
Filter, Map and Reduce functions in Javascript
Closure in Javascript
Optional chaining operator in Javascript
Consoling in table format in javascript
Fetch API in Javascript
HTML web Storage API
Checking the online or offline status of the browser

Nullish coalescing operator(??) in Javascript

Published on: February 02, 2021 By T.Andrew Rayan

In this article, we shall see what is nullish coalescing operator? and how to use it to handle a variable that is null or undefined.

This operator is represented with the two question marks ??.

The expression, a??b; will return the value of a if it is defined and not null, else it will return the value of b.

Example

       
let b = 10;
let a;
a??b;

Output

10

Here the variable a is declared but it's not defined with any value. So it will return the value of b.

If we rewrite the above example as below,

       
let b = 10;
let a=null;
a??b;

Output

10

Since the value of a is null it will return the value of b.

So the operator ?? is shortcut representation of the following

(a!==undefined && a!==null)? a:b;

The main use of this nullish coalescing operator ?? is to provide some default value if the value of the variable is undefined.

Example

       
let currency;
console.log(currency??'USD'); 

This will return USD since the currency is not defined with any value.

We can also check multiple condition like below,

       
let x,y,z;
x??y??z??'Default';

This will return the value Default.

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