TypeScript optional generic in type

Question

I'm curious could I make this generic optional somehow?

export type RequestType<T> = {
  readonly type: string;
  readonly value: string | T;
};

Because when I try to set object' type to RequestType it returns an error, that generic type requires 1 type argument.

Nicholas Tower · Accepted Answer · 2021-06-29 19:44:56Z

1

You can provide a default type for T. For example:

export type RequestType<T = boolean> = {
  readonly type: string;
  readonly value: string | T;
}

The default value can even be string if you like, and thus value will be string | string, also known as just string.

answered Jun 29, 2021 at 19:38

Nicholas Tower

87k10 gold badges115 silver badges127 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

I could, but I don't want to. I want it to remain string | T or just string.

@Cholewka You can set the default type to never to get that behavior.

or just string Then default it to string or never

Thank you, that's what I've been looking for :)