Reference the Constructor of a Type in TypeScript (Generically)

Although not initially intuitive, I run into this issue while documenting the register function in Marty.js. I didn't realise a solution, so I reached out to a friend who provided me with this beauty.

function register<T>(clazz: { new (...args: any[]): T }): T;

And it works brilliantly! But what's this even doing? I've just created a generic function that accepts a constructor function of any type and returns that type. No need to do type coercion. It turned out perfectly for this situation, where I can register a Store, Queries, ActionCreators and more!

You can also write this with a slightly different syntax such as new (...args: any[]) => T. There's no real difference here.

Although it doesn't apply here, we can also look how we might accept more specific types of constructors.

// Using `typeof`...

class X {
  method(): void {}
}

function create(C: typeof X) {
  return new C();
}

create(X);

// Using an inline parameter...

interface Y {
  method(): void;
}

function create2(C: new (...args: any[]) => Y) {
  return new C();
}

class Z implements Y {
  method(): void {}
}

create2(Z);