js之手写promise.all

let p1 = new Promise((resolve, reject)=>{
    
    
    setTimeout(()=>{
    
    
      resolve(1)
    },1000)
  })
  p1.then((res)=>{
    
    
    console.log(res)
  }).catch((err)=>{
    
    
    console.log(err);
  })

  let p2 = new Promise((resolve, reject)=>{
    
    
    setTimeout(()=>{
    
    
      resolve(2)
    },1000)
  })
  p2.then((res)=>{
    
    
    console.log(res)
  }).catch((err)=>{
    
    
    console.log(err);
  })


  let p3 = new Promise((resolve, reject)=>{
    
    
    setTimeout(()=>{
    
    
      resolve(3)
    },1000)
  })
  p3.then((res)=>{
    
    
    console.log(res)
  }).catch((err)=>{
    
    
    console.log(err);
  })
  //
  // let pAll = Promise.all([p2,p3,p1]).then((res)=>{
    
    
  //   console.log(res)
  // })

  Promise._all = function (promiseArr) {
    
    
    // 转成数组
    let newPromiseArr = Array.from(promiseArr)
    //数组长度
    let len = newPromiseArr.length
    let num = 0
    let result = []
    return new Promise((resolve,reject)=>{
    
    
      newPromiseArr.forEach((value, index)=>{
    
    
         Promise.resolve(value).then((res)=>{
    
    
          result[index] = res
          if(++num === len) resolve(result)
        }).catch((err)=>{
    
    
          reject(err)
         })
      })
    })

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