EventEmitter

class EventEmitterDemo {
  constructor() {
    this.events = {}; // 映射事件名和处理函数
  }
  // 将处理函数添加到事件的回调队列后
  on(name, cb) {
    if (!this.events[name]) {
      this.events[name] = [];
    }
    this.events[name].push(cb);
  }
  // 将处理函数添加到事件的回调队列前
  prependListener(name, cb) {
    if (!this.events[name]) {
      this.events[name] = [];
    }
    this.events[name].unshift(cb);
  }
  // 触发事件，执行回调函数
  emit(name, args = "") {
    for (let cb of this.events[name]) {
      cb(args);
    }
  }
  // 移除某一个回调函数
  off(name, cb) {
    let cbs = this.events[name];
    let cbIndex = cbs.indexOf(cb);
    if (cbIndex !== -1) {
      this.events[name].splice(cbIndex, 1);
    }
  }
  // 为指定事件注册一个单次监听器，监听器至多只会触发一次，触发后立即解除该监听器
  once(name, cb) {
    let onceCb = (...argvs) => {
      cb(...argvs);
      this.off(name, onceCb);
    };
    this.on(name, onceCb);
  }
}

// const EventEmitter = require('events');
let event = new EventEmitterDemo();
let demoFunc = function () {
  // 绑定事件和处理函数
  console.log("demo boom!");
};
let demo2Func = function () {
  console.log("demo2 boom!");
};
let demo3Func = function () {
  console.log("demo3 boom!");
};
event.once("demo", demoFunc);
event.on("demo", demo2Func);
event.prependListener("demo", demo3Func);
event.off("demo", demo2Func);
console.log("set fire to demo");
setTimeout(function () {
  event.emit("demo");
}, 1000);
setTimeout(function () {
  event.emit("demo");
}, 2000);

手写 eventbus，参考

• 手写 eventbus