@discoveryjs/discovery/lib/core/emitter.js

Frontend framework for rapid data (JSON) analysis, shareable serverless reports and dashboards

export class Emitter {
  listeners;
  constructor() {
    this.listeners = /* @__PURE__ */ Object.create(null);
  }
  on(event, callback) {
    this.listeners[event] = {
      callback,
      next: this.listeners[event] || null
    };
    return this;
  }
  once(event, callback) {
    return this.on(event, function wrapper(...args) {
      callback.apply(this, args);
      this.off(event, wrapper);
    });
  }
  off(event, callback) {
    let cursor = this.listeners[event] || null;
    let prev = null;
    while (cursor !== null) {
      if (cursor.callback === callback) {
        cursor.callback = null;
        if (prev) {
          prev.next = cursor.next;
        } else {
          this.listeners[event] = cursor.next;
        }
        break;
      }
      prev = cursor;
      cursor = cursor.next;
    }
    return this;
  }
  emit(event, ...args) {
    let cursor = this.listeners[event] || null;
    let hadListeners = false;
    while (cursor !== null) {
      if (typeof cursor.callback === "function") {
        cursor.callback.apply(this, args);
      }
      hadListeners = true;
      cursor = cursor.next;
    }
    return hadListeners;
  }
}