Typescript interface generics

Question

Could someone help me understand what T = {} means in the following typescript interface? I cannot find docs indicating such usage. How is it different from just T ?

interface CustomProps<T = {}> {
      itemId: string;
      id: string;
}

Answer 1

They're called generic parameter defaults and were introduced in TypeScript 2.3. You can find the documentation here .

For your example, it means that if no type parameter is specified, it will default to {} , which is commonly referred to as the empty object type .