Double Question Marks (??) Explained in Typescript

May 4, 2023Arkar

Typescript

In TypeScript, the double question mark (??) is known as the nullish coalescing operator. It is used to provide a default value for a variable that may be null or undefined.

const userName: string | null = null;
const defaultName = "Guest";
const displayName = userName ?? defaultName;
console.log(displayName); // Output: "Guest"


const count: number | null = 0;
const defaultCount = 10;

const usingOr = count || defaultCount; // 10
const usingNullish = count ?? defaultCount; // 0

console.log(usingOr); // Output: 10
console.log(usingNullish); // Output: 0