class EventHub {

  constructor() {

    // 调度中心

    this.channel = {}

  }

​

  on(name, fn) {

    this.channel[name] = this.channel[name] || []

    this.channel[name].push(fn)

  }

​

  off(name, fn) {

    const list = this.channel[name] || []

    const index = list.indexOf(fn)

    if(index < 0) return

    list.splice(index, 1)

  }

​

  once(name, fn) {

    this.channel[name] = this.channel[name] || []

    let one = (arg) => {

      fn.call(null, arg)

    }

    // 记录下绑定事件

    one.fn = fn

    // 添加移除方法

    one.off = () => { this.off(name, one) }

    this.on(name, one)

  }

​

  emit(name, data) {

    let list = this.channel[name] || []

    let ones = []

    list.forEach(fn => {

      fn.call(null, data)

      fn.off && ones.push(fn)

    })

    // 移除once订阅事件、执行完再移除不会导致删除数组后执行顺序不对问题

    ones.forEach(fn => fn.off())

  }

}

​

let q = new EventHub()

q.on('click', function(data) {

  console.log('on')

})

q.once('click', function(data) {

  console.log('once')

})

​

q.emit('click')

q.emit('click')

​