ES6 13 手写 Promise

首先写一个原始的 Promise

let OP = new promise((res,rej) =>{
    res(0)
})
op.then((val) =>{
    console.log(val)
},(rej) =>{
    console.log(reason)
})

ES5 模拟

function MyPromise(executor){
  this.status = 'pending';
  var _self = this;
  _self.resolveValue = null;
  _self.rejectValue = null;
  function resolve(val){
    if(_self.status == 'pending'){
      _self.status = 'Fulfilled';
      _self.resolveValue = val
    }
  }
  function reject(reason){
      if(_self.status == 'pending'){
      _self.status = 'Rejected';
      _self.rejectValue = reason;
    }
  }
  try{
      executor(resolve, reject);
  }catch(e){
      reject(e);
  }
    executor(resolve, reject);
}
MyPromise.prototype.then = function(onFulfilled,onRejected){
    var self = this;
  if(self.status == 'Fulfilled'){
     onFulfilled(_self.resolveValue);
  }
  if(self.status == 'Rejected'){
     onRejected(_self.rejectValue);
  }
}

异步操作

function MyPromise(executor){
  this.status = 'pending';
  var _self = this;
  _self.resolveValue = null;
  _self.rejectValue = null;
  _self.ResolveCallBackList = [];
  _self.RejectCallBackList = [];
  function resolve(val){
    if(_self.status == 'pending'){
      _self.status = 'Fulfilled';
      _self.resolveValue = val
      _self.ResolveCallBackList.forEach(function(ele){
          ele();
      })
    }
  }
  function reject(reason){
      if(_self.status == 'pending'){
      _self.status = 'Rejected';
      _self.rejectValue = reason;
      _self.RejectCallBackList.forEach(function(ele){
          ele();
      })
    }
  }
  try{
      executor(resolve, reject);
  }catch(e){
      reject(e);
  }
    executor(resolve, reject);
}
MyPromise.prototype.then = function(onFulfilled,onRejected){
    var self = this;
  if(self.status == 'Fulfilled'){
     onFulfilled(_self.resolveValue);
  }
  if(self.status == 'Rejected'){
     onRejected(_self.rejectValue);
  }
  //
  if(self.status == 'pending'){
      self.ResolveCallBackList.push(function(){
        onFulfilled(_self.resolveValue);
    })
    self.RejectCallBackList.push(function(){
        onRejected(_self.rejectValue);
    })
  }
}

链式调用

function MyPromise(executor){
  this.status = 'pending';
  var _self = this;
  _self.resolveValue = null;
  _self.rejectValue = null;
  _self.ResolveCallBackList = [];
  _self.RejectCallBackList = [];
  function resolve(val){
    if(_self.status == 'pending'){
      _self.status = 'Fulfilled';
      _self.resolveValue = val
      _self.ResolveCallBackList.forEach(function(ele){
          ele();
      })
    }
  }
  function reject(reason){
      if(_self.status == 'pending'){
      _self.status = 'Rejected';
      _self.rejectValue = reason;
      _self.RejectCallBackList.forEach(function(ele){
          ele();
      })
    }
  }
  try{
      executor(resolve, reject);
  }catch(e){
      reject(e);
  }
    executor(resolve, reject);
}
MyPromise.prototype.then = function(onFulfilled,onRejected){
    var self = this;
  var nextPromise = new MyPromise(function(res, rej){
       if(self.status == 'Fulfilled'){
             var nextResolveValue = onFulfilled(_self.resolveValue);
               res(nextResolveValue)
      }
      if(self.status == 'Rejected'){
             var nextRejectValue = onRejected(_self.rejectValue);
            res(nextRejectValue);
      }
      //
      if(self.status == 'pending'){
        self.ResolveCallBackList.push(function(){
          var nextResolveValue = onFulfilled(_self.resolveValue);
               res(nextResolveValue)
        })
        self.RejectCallBackList.push(function(){
          var nextRejectValue = onRejected(_self.rejectValue);
            res(nextRejectValue);
        })
      }
  })
  return nextPromise;
}