手写发布订阅类

class Sub {
  events = {};

  on(type, func) {
    !Array.isArray(this.events[type]) ? (this.events[type] = []) : null;
    let arr = this.events[type];
    if (arr.includes(func)) return;
    arr.push(func);
  }

  off(type, func) {
    let arr = this.events[type];
    let item = null;
    if (!Array.isArray(this.events[type])) {
      throw new TypeError(`${type} 自定义事件在事件池中并不存在!`);
    }
    for (let i = 0; i < arr.length; i++) {
      item = arr[i];
      if (item === func) {
        // 这样只是让集合中当前项值变为null，但是集合的机构是不发生改变的「索引不变」；
        // 下一次执行emit的时候，遇到当前项是null，我们再去把其移除掉即可；
        arr[i] = null;
        break;
      }
    }
  }

  emit(type, ...params) {
    let arr = this.events[type];
    let item = null;
    for (let i = 0; i < arr.length; i++) {
      item = arr[i];
      if (typeof item === "function") {
        item(...params);
        continue;
      }
      //不是函数的值都移除掉即可
      arr.splice(i, 1);
      i--;
    }
  }
}

const sub = new Sub();

const fn1 = () => console.log(1);
const fn2 = () => console.log(2);
const fn3 = () => {
  console.log(3);
  sub.off("A", fn1);
  sub.off("A", fn2);
};
const fn4 = () => console.log(4);
const fn5 = () => console.log(5);
const fn6 = () => console.log(6);

sub.on("A", fn1);
// sub.on("A", fn1);
sub.on("A", fn2);
sub.on("A", fn3);
sub.on("A", fn4);
sub.on("A", fn5);
sub.on("A", fn6);
setTimeout(() => {
  sub.emit("A");
}, 1000);

setTimeout(() => {
  sub.emit("A");
}, 2000);