@wordpress/data/build-module/utils/emitter.js

Data module for WordPress.

/**
 * Create an event emitter.
 *
 * @return {import("../types").DataEmitter} Emitter.
 */
export function createEmitter() {
  let isPaused = false;
  let isPending = false;
  const listeners = new Set();

  const notifyListeners = () => // We use Array.from to clone the listeners Set
  // This ensures that we don't run a listener
  // that was added as a response to another listener.
  Array.from(listeners).forEach(listener => listener());

  return {
    get isPaused() {
      return isPaused;
    },

    subscribe(listener) {
      listeners.add(listener);
      return () => listeners.delete(listener);
    },

    pause() {
      isPaused = true;
    },

    resume() {
      isPaused = false;

      if (isPending) {
        isPending = false;
        notifyListeners();
      }
    },

    emit() {
      if (isPaused) {
        isPending = true;
        return;
      }

      notifyListeners();
    }

  };
}
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