手写promise的实现

function myPromise(excutor){ // 用self来接收this let self = this // 定义初始状态 self.status = 'pending' // 定义成功的信息 self.success = null // 定义失败的信息 self.fail = null

  // 定义缓存
  self.onFulfilledCallbacks = []
  self.onRejectedCallbacks = []

  // 成功的回调
  function reslove(value){
    if(self.status == 'pending'){
      self.status = 'fulfilled'
      self.success = value

      self.onFulfilledCallbacks.forEach(item => item(value))
    }
  }

  // 失败的回调
  function reject(error){
    if(self.status == 'pending'){
      self.status = 'rejected'
      self.fail = error

      self.onRejectedCallbacks.forEach(item => item(error))
    }
  }

  try {
    // 立即执行
    excutor(reslove,reject)
  } catch (error) {
    reject(error)
  }
}

// 在原型上定义then方法
myPromise.prototype.then = function(onFulfilled,onRejected){
  onFulfilled =typeof onFulfilled === 'function' ? onFulfilled : function(onFulfilled){reslove(onFulfilled)}
  onRejected = typeof onRejected === 'function' ? onRejected : function(onRejected){throw 'error'}
  
  let self = this
  self.onFulfilledCallbacks.push(onFulfilled)
  self.onRejectedCallbacks.push(onRejected)

}