SOURCE

function Promize (executor) {
	return new _Promize (executor)
}

function _Promize (executor) {
    this.STATUS = {
        PENDING: 'Pending', // 等待态
        FULFILLED: 'Fulfilled', // 执行态
        REJECTED: 'Rejected' // 拒绝态
    }
    
    this.status = this.STATUS.PENDING
    this.thenQueue = []
    this.catchExecutor = null
    // 保证链式操作以后才执行
    setTimeout(() => {
        try {
            executor(this.resolve.bind(this), this.reject.bind(this))
        } catch (err) {
            this.reject.call(this, err)
        }
    },0)
}

_Promize.prototype.resolve = function (data) {
  	if (this.status === this.STATUS.PENDING) {
      this.stauts = this.STATUS.FULFILLED
      let thenTask = this.thenQueue.shift()
      if (thenTask) {
      	this.callbackData = data
      	thenTask()
      }
    }
}

_Promize.prototype.reject = function (err) {
  if (this.catchExecutor) {
    this.catchExecutor(err)
  }
}

_Promize.prototype.catch = function (errorExecutor) {
	this.catchExecutor = errorExecutor
  return this
}

_Promize.prototype.then = function (task) {
 	this.thenQueue.push(() => {
    let res = task(this.callbackData)
    if (res) {
      this.callbackData = res
    }
    this.next()
  }) 
  // 链式调用
  return this
}

_Promize.prototype.next = function () {
  if (this.thenQueue.length > 0) {
    let thenTask = this.thenQueue.shift()
    thenTask()
  }
}

Promize(function(resolve, reject){
  setTimeout(() => {
    console.log('done')
    throw new Error('hi')
    resolve('123')
  },2000)
}).then((data) => data+'2')
  .then((data) => console.log(data))
  .catch((err) => console.log('err:'+ err))