success/packages/excalidraw/emitter.ts

import type { UnsubscribeCallback } from "./types";

type Subscriber<T extends any[]> = (...payload: T) => void;

export class Emitter<T extends any[] = []> {
  public subscribers: Subscriber<T>[] = [];

  /**
   * Attaches subscriber
   *
   * @returns unsubscribe function
   */
  on(...handlers: Subscriber<T>[] | Subscriber<T>[][]): UnsubscribeCallback {
    const _handlers = handlers
      .flat()
      .filter((item) => typeof item === "function");

    this.subscribers.push(..._handlers);

    return () => this.off(_handlers);
  }

  once(...handlers: Subscriber<T>[] | Subscriber<T>[][]): UnsubscribeCallback {
    const _handlers = handlers
      .flat()
      .filter((item) => typeof item === "function");

    _handlers.push(() => detach());

    const detach = this.on(..._handlers);
    return detach;
  }

  off(...handlers: Subscriber<T>[] | Subscriber<T>[][]) {
    const _handlers = handlers.flat();
    this.subscribers = this.subscribers.filter(
      (handler) => !_handlers.includes(handler),
    );
  }

  trigger(...payload: T) {
    for (const handler of this.subscribers) {
      handler(...payload);
    }
    return this;
  }

  clear() {
    this.subscribers = [];
  }
}