模式实现vue事件总线

前言：发布订阅模式，还具有解除订阅功能

模拟实现

function fn1(n1, n2) {console.log('first add', n1, n2)}
function fn2(n1, n2) {console.log('second add', n1, n2)}
function fn3(n1, n2) {console.log('third add', n1, n2)}

class MYVue {
  constructor() {
    this._events = Object.create(null) // 存放各种自定义事件的对象
  }
  $on(event, fn) {
    if (Array.isArray(event)) {
      event.forEach(v => {this.$on(v, fn)})
    } else {
      if (!this._events[event]) this._events[event] = []
      this._events[event].push(fn)
    }
  }
  $off(event, fn) {
    if (!arguments.length) { // 移除所有事件
      this._events = Object.create(null)
      return
    }
    if (Array.isArray(event)) {
      event.forEach(v => {this.$off(v, fn)})
      return
    }
    const item = this._events[event]
    if (!item) return
    if (!fn) { // 移除某个事件所有订阅的函数
      this._events[event] = null
      return
    }
    const it = item.findIndex(v => v === fn)
    if (it !== -1) item.splice(it,1)
  }
  $once(event, fn) {
    function on() {
      this.$off(event, on)
      fn.apply(this, arguments)
    }
    on.fn = fn
    this.$on(event, on)
  }
  $emit(event) {
    let item = this._events[event]
    if (!item) return
    item.forEach(fn => {
      fn.apply(this, [...arguments].slice(1))
    })
  }
}

const myvue = new MYVue()
myvue.$on('first',fn1)
myvue.$on('second',fn2)
myvue.$once('third',fn3)
myvue.$emit('first', 20, 30)
myvue.$emit('second', 60, 70)
myvue.$emit('third', 100, 200)