Type-safe event hooks in Typescript

event-hooks.ts

type Handler<TEvent> = (event: TEvent) => void;

interface Hook<TEvent> {
  (handler: Handler<TEvent>): void;
  send(event: TEvent): void;
}

function hook<TEvent>(): Hook<TEvent> {
  const handlers: Array<Handler<TEvent>> = [];

  const fn = function (handler: Handler<TEvent>) {
    handlers.push(handler);
  };

  return Object.assign(
    fn,
    {
      send(event: TEvent) {
        for (var i = 0; i < handlers.length; i++) {
          handlers[i](event);
        }
      }
    }
  )
}

// EXAMPLE:

interface LoginEvent {
  username: string;
  success: boolean;
}

class UserModel {
  onLogin = hook<LoginEvent>();
}

var model = new UserModel();

// register an event listener:
model.onLogin(event => console.log(event));

// send an event:
model.onLogin.send({ username: 'Rasmus', success: true });