How to determine type of callback's input parameters in typescript

Question

I have an function:

const myFunc = (callback: (...params: any) => void, params: [any]): void => {
   callback(...params);
};
//sample of using
myFunc((name: string) => { console.log(name) }, ["Mark"])

The myFunc takes callback and parameters. How to avoid "any" and provide that params in both case have same type? p.s. (callback: (...params: T) => void, params: [T]) = doesn't work...

Do all parameters have the same type? Do you expect the same number of parameters? — Robby Cornelissen
– Robby Cornelissen, Commented May 31, 2022 at 3:19
yes - all parameters will have same type, number of parameters can by dynamic. — Nikita Polevoy
– Nikita Polevoy, Commented May 31, 2022 at 3:24

Robby Cornelissen · Accepted Answer · 2022-05-31 03:26:16Z

1

You can use a variadic tuple type:

const myFunc = <T extends unknown[]>(
  callback: (...params: T) => void,
  params: T
): void => {
   callback(...params);
};

myFunc((name: string) => {}, ["Mark"]); // OK
myFunc((name: string, age: number) => {}, ["Mark", 23]); // OK

myFunc((name: string) => {}, ["Mark", 23]); // Error
myFunc((name: string, city: string) => {}, ["Mark", 23]); // Error

If you know all parameters to be of the same type, you can use that type (e.g. string) instead of unknown.

answered May 31, 2022 at 3:26

Robby Cornelissen

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