README.md

About

A type safe event target implementation.

Creation

type Events = 
  | Event<'start', StartType>
  | Event<'stop', StartType>;
  
const target = new EventTarget<Events>();

Add event listener

target.addEventListener('start', startHandler);

Remove event listener

target.removeEventListener('start', startHandler);

Dispatch event

Note: A slight deviation from the JS standard EventTarget

target.dispatchEvent('start', payload);

EventTarget.ts

export type Event<K extends string = string, V extends any = any> = {
  key: K;
  value: V;
};

export class EventTarget<T extends Event> {
  private listeners: { [key in T["key"]]?: Array<(event: any) => void> } = {};

  public addEventListener<K extends T["key"]>(
    type: K,
    handler: (event: EventValue<T, K>) => void
  ) {
    this.listeners[type] = [...(this.listeners[type] || []), handler];
  }

  public removeEventListener<K extends T["key"]>(
    type: K,
    handler: (event: EventValue<T, K>) => void
  ) {
    if (!this.listeners[type]) {
      return;
    }

    this.listeners[type] = this.listeners[type].filter((l) => l !== handler);
  };

  public dispatchEvent<K extends T["key"]>(type: K, event: EventValue<T, K>) {
    this.listeners[type].forEach((handler) => handler(event));
  };
};