发布订阅模式

实现一个发布订阅模式拥有 on emit once off 方法。

class EventEmitter {
  constructor() {
    this.events = {}
  }
  // 实现订阅
  on(type, callback) {
    if (!this.events[type]) {
      this.events[type] = [callback]
    } else {
      this.events[type].push(callback)
    }
  }
  // 删除订阅
  off(type, callback) {
    if (!this.events[type]) {
      return
    }
    this.events[type] = this.events[type].filter((item) => {
      return item !== callback
    })
  }
  // 值执行一次订阅
  once(type, callback) {
    function fn() {
      callback()
      this.off(type, fn)
    }
    this.on(type, fn)
  }
  // 触发事件
  emit(type, ...rest) {
    this.events[type] && this.events[type].forEach((fn) => fn.apply(this, rest))
  }
}

测试

const event = new EventEmitter()

const handle = (rest) => {
  console.log(rest)
}

event.on('click', handle)
event.emit('click', 1, 2, 3, 4) // [1,2,3,4]

event.off('click', handle)
event.emit('click', 1, 2)

event.once('dbClick', () => {
  console.log(123456)
})
event.emit('dbClick') // 123456
event.emit('dbClick')