Passing a generic function in as a callback in Typescript

Question

I'm trying to preserve the type information of arguments to a callback, where the callback is a generic:

function Foo<Template>(argument: Template) {
  // Do something with argument
}

function Bar(callback: Function) {
  callback('something')
}

let x = Bar( Foo<String> )

This does not look like valid typescript syntax. Any way to do this?

Answer 1

Expanding on the answer of Rodrigo here. If you have a function with a generic:

function doSomething<T>(t: T): void {
    console.log("oh " + t);
}

You can define the type of the function as follows:

type Handler = <T>(t: T) => void;

Then you can use the type Handler as a function parameter:

function thisFirst(callback: Handler) {
  callback<string>('boink');
}

thisFirst(doSomething)

Answer 2

You can define a generic function for callback with a generic argument like this:

const handleSomething =
  <T extends (...args: Parameters<T>) => ReturnType<T>>(callback: T) =>
  (...args: Parameters<T>) =>
    callback(...args)