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

• MDN Web Docs