手写EventEmitter事件巴士

Copy 
1class EventEmitter {
2  constructor() {
3    this.events = {};
4  }
5  on(name, fn) {
6    if (!this.events[name]) {
7      this.events[name] = [];
8    }
9    this.events[name].push(fn);
10    return this;
11  }
12  emit(name, ...args) {
13    if (!this.events[name]) {
14      console.log("没有注册这个事件");
15      return this;
16    }
17    this.events[name].forEach((fn) => fn.apply(this, args));
18    return this;
19  }
20  once(name, fn) {
21    //包一层多做一步off
22    const func = (...args) => {
23      this.off(name, func);
24      fn.apply(this, args);
25    };
26    this.on(name, func);
27    return this;
28  }
29  off(name, fn) {
30    if (!this.events[name]) {
31      return this;
32    }
33    //如果不指定fn,那么全部移除掉
34    if (!fn) {
35      delete this.events[name];
36      return this;
37    }
38    //如果指定了fn,那么移除对应的fn
39    const index = this.evnets[name].indexOf(fn);
40    this.evnets[name].splice(index, 1);
41    return this;
42  }
43}

Copy 
1const eventEmitter = new EventEmitter();
2eventEmitter.on("test", (args) => {
3  console.log(args);
4});
5eventEmitter.emit("test", { a: 1 });