Observable class for typescript

observable.ts

/**
 * Simple class for managing callable observers.
 */
export class Observable<Fn extends (...args) => any> {
    private observers: Set<Fn> = new Set();

    add(o: Fn): void {
        this.observers.add(o);
    }

    remove(o: Fn): void {
        this.observers.delete(o);
    }

    notify(...args: Parameters<Fn>) {
        for (const o of this.observers) {
            o(...args);
        }
    }
}

Observers are stored using a Set so adding the same observer multiple times has no effect. As per the ECMA spec, notify() will iterate through the observers in the order they were added.

// The function signature we expect when calling observable.notify()
type fn = (a: string, b: number) => void;

// A simple observer that prints its arguments
const o: fn = (a: string, b: number) => console.log(a, b);
const observable = new Observable<fn>();


observable.add(o);
observable.add(o); // does nothing
observable.notify("helloworld", 1234);  // calls o once

observable.remove(o);
observable.notify("helloworld", 1234);  // does not call o