Example TypeScript Event System

signal.ts

/**
MIT License

Copyright (c) 2022 Davide Aversa

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

import * as _ from "lodash"

interface SignalBindingAsync<S, T> {
    listener?: string;
    handler: (source: S, data: T) => Promise<void>;
}

interface IAsyncSignal<S,T> {
    bind(listener: string, handler: (source: S, data: T) => Promise<void>): void;
    unbind(listener: string): void;
}

class AsyncSignal<S, T> implements IAsyncSignal<S,T> {
    private handlers: Array<SignalBindingAsync<S, T>> = [];

    public bind(
        listener: string,
        handler: (source: S, data: T) => Promise<void>,
    ): void {
        if (this.contains(listener)) {
            this.unbind(listener);
        }
        this.handlers.push({ listener, handler });
    }

    public unbind(listener: string): void {
        this.handlers = this.handlers.filter(h => h.listener !== listener);
    }

    public async trigger(source: S, data: T): Promise<void> {
        // Duplicate the array to avoid side effects during iteration.
        this.handlers.slice(0).map(h => h.handler(source, data));
    }

    public async triggerAwait(source: S, data: T): Promise<void> {
        // Duplicate the array to avoid side effects during iteration.
        const promises = this.handlers.slice(0).map(h => h.handler(source, data));
        await Promise.all(promises);
    }

    public contains(listener: string): boolean {
        return _.some(this.handlers, h => h.listener === listener);
    }
    
    public expose(): IAsyncSignal<S,T> {
        return this
    }
}

class Dog {
    private readonly onBark = new AsyncSignal<Dog, string>();
	
	constructor(readonly name: string) {}

    public get BarkEvent(): IAsyncSignal<Dog, string> {
        return this.onBark.expose();
    }
	
	public sayWof() {
		this.onBark.trigger(this, "WOF!");
	}

	public sayAnything(message: string) {
		this.onBark.trigger(this, message);
	}
}

class DogListener {

	constructor(dog: Dog) {
		let dogBarkHandler = async (s: Dog, bark: string) => {
			console.log(`Listener: Dog "${dog.name}" barked: ${bark}`);
            return;
		}
		dog.BarkEvent.bind("dogBark", dogBarkHandler);

        // NOW I MAKE THE DOG BARK!
        // This cannot compile!
        // dog.BarkEvent.trigger(dog, "FAKE WOOF!")
	}
	
}

const apollo = new Dog("Apollo");
const apolloListener = new DogListener(apollo);

apollo.sayWof()