TypeScript 7 reference · Utility Types

TypeScript Parameters<Type> Utility Type

Get a function's parameter types as a tuple, useful for wrappers that pass arguments through.

TypeScript 7 Since 3.1

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Syntax

Parameters<Type>

Parameters

Parameter	Description
`Type`	A function type.

Return value

A tuple type.

Examples

A tuple of the parametersTry it yourself

function sendEmail(to: string, subject: string, urgent: boolean) {
  return `${urgent ? "URGENT " : ""}${subject} -> ${to}`;
}
type EmailArgs = Parameters<typeof sendEmail>; // [string, string, boolean]
const args: EmailArgs = ["[email protected]", "Hi", false];
console.log(sendEmail(...args));

Output

Hi -> [email protected]

Typed wrappersTry it yourself

function logged<F extends (...a: any[]) => any>(fn: F) {
  return (...args: Parameters<F>): ReturnType<F> => {
    console.log("calling with", args);
    return fn(...args);
  };
}
const add = logged((a: number, b: number) => a + b);
console.log(add(2, 3));