Timur Dautov | Frontend Engineering Blog
#frontend#js
by Timur Dautov

What is Nullish Coalescing in JavaScript

Nullish Coalescing is an operator introduced in JavaScript ES2020. It is represented by two question marks ??. It is used to provide a default value when the value is null or undefined.

Example

const name = null;
const username = name ?? 'Guest';
console.log(username); // Guest

In the above example, the name variable is null, so the username variable will be assigned the value Guest.

Difference between Nullish Coalescing and Logical OR Operator#

The Nullish Coalescing operator ?? is similar to the Logical OR operator ||, but with a key difference.

The Logical OR operator || will return the right-hand side value if the left-hand side value is falsy: false, 0, ' ', null, undefined, NaN.

const name = '';
const username = name || 'Guest';
console.log(username); // Guest

The Nullish Coalescing operator ?? will return the right-hand side value only if the left-hand side value is null or undefined.

const name = '';
const username = name ?? 'Guest';
console.log(username); // ''

Summary#

  • The Nullish Coalescing operator ?? is a useful operator in JavaScript to provide a default value when the value is null or undefined.
  • It is similar to the Logical OR operator ||, but with a key difference. The Nullish Coalescing operator ?? will return the right-hand side value only if the left-hand side value is null or undefined.

References#