Parameters

Extract function parameter types like a pro! 📤

In this easy-level challenge, you'll implement TypeScript's built-in Parameters<T> utility type from scratch. This type extracts the parameter types from a function type and returns them as a tuple. It's an essential tool for working with functions at the type level.

You'll learn how to use conditional types with infer to capture function parameters, a technique that opens the door to powerful function type manipulations in TypeScript.

For this challenge, you will need to change the following code to make the tests pass (no type check errors).

const foo = (arg1: string, arg2: number): void => {}
 
type FunctionParamsType = MyParameters<typeof foo> // [arg1: string, arg2: number]

Detailed Explanation

The Parameters type uses conditional types with infer to extract function parameters.

type MyParameters<T extends (...args: any[]) => any> = T extends (
  ...args: infer Params
) => any
  ? Params
  : false

Breaking it down:

• T extends (...args: any[]) => any constrains T to function types
• infer P captures the parameter types as a tuple
• If T matches the function pattern, return P
• Otherwise, return never (though this shouldn't happen due to the constraint)

This pattern is fundamental for introspecting function types and is used extensively in TypeScript's utility types and advanced type programming.