15.Promise及手写

1.Promise用法

function silentLogin(){
  return new Promise(async (resolve,reject) => {
         let res = await apiLogin({'data':totalData.resdatapost,})
          if(res.code ==200){
               resolve(res.data);
          }else{
              reject(res.data);
          }
  })
}
silentLogin().then(res =>{}).catch(err =>{})

2.手写Promise

   function MyPromise(executor) {
               this.status = 'padding' // 定义初始状态
               this.value = undefined // 定义初始值
               this.onResolvedCallbacks = []   // 存放成功的回调
               this.onRejectedCallbacks= []  // 存放失败的回调
               let resolve = (value) => {
                 if (this.status === 'padding') {
                   this.status = 'resolve'
                   this.value = value
                    // 依次将对应的函数执行
                   this.onResolvedCallbacks.forEach(fn=>fn());
                 }
               }
             let reject = (value) =>{
               if (this.status === 'padding') {
                 this.status = 'reject'
                 this.value = value
                 // 依次将对应的函数执行
                this.onRejectedCallbacks.forEach(fn=>fn());
               }
             }
           try {
             executor(resolve, reject)
            } catch (reason) {
             reject(reason);
            }
      }
      // 定义 then 方法
      MyPromise.prototype.then = function(onResolve, onReject) {
        switch(this.status){
            case 'padding':
         //如果promise的状态是 pending，需要将 onFulfilled 和 onRejected 函数存放起来，
          //等待状态确定后，再依次将对应的函数执行
                this.onResolvedCallbacks.push(() => {
                   onResolve(this.value)
                 });
                this.onRejectedCallbacks.push(() => {
                   onReject(this.value)
                 });
              break;
            case 'resolve' :
              onResolve(this.value)
              break;
            case 'reject':
              onReject(this.value)
              break;
             default:
        }
      }
      //测试
      new MyPromise((resolve, reject) => {
           setTimeout(() => {
              resolve('成功')
           },1500)
         })
         .then(res => {
           console.log('res',res)
         }, err => {
           console.log('err',err)
         })

3.Promise.all用法

   Promise.all([p3,p1,p2]).then(res =>{
         console.log(444,res)
     })

4.手写Promise.all

 function myPromiseAll(promises){
         return new Promise((resolve,reject) => {
              if(!Array.isArray(promises)){
    throw new TypeError("promises must be an array but it resolved to " + typeof(promises))
                  }
                  let result = []
                  let count = 0
              promises.forEach((item,index) => {
                    item.then((res) =>{
                             result[index] = res
                                   count++
                          if(count === promises.length){
                              resolve(result)
                          }
                    },
                    (err) =>{
                           reject(err)
                    }
                    )
              })
          })
        }

     // 测试Promise.All
     const p1 = new Promise((reslove,reject)=>{
          setTimeout(function(){
               reslove(1)
          },1000)
     })
     const p2 = new Promise((reslove,reject)=>{
          setTimeout(function(){
               reslove(2)
          },2000)
     })
     const p3 = new Promise((reslove,reject)=>{
          setTimeout(function(){
               reslove(3)
          },3000)
     })
     myPromiseAll([p3,p1,p2]).then(res=>{
          console.log(res)  //[3,1,2]
     })