all的要保证顺序的话是不是可以这样   Promise._all = (arr) => {             return new Promise((resolve, reject) => {                 arr = [...arr]//将可迭代对象变为数组                 let ans = []                 let count = 0                 for (let i = 0; i < arr.length; i++) {                     //并行开启                     Promise.resolve(arr[i]).then((val) => {//不用push保存用下标保证顺序                         count++                         ans[i] = val                         if (count === arr.length) {                             resolve(ans)                         }                     }).catch((e) => {                         reject(e)                     })                 }             })         }