Promise.all不等待完成内部Promise.all完成

Question

let obj = [
  {
    Id: 1,
    name: 'david',
    Address:[{
      city: 'dubai',
      country: 'UAE'
    }]
  },
  {
    Id: 2,
    name: 'Ram',
    Address: [{
      city: 'US',
      country: 'India'
    },
    {
      city: 'Delhi1',
      country: 'India1'
    }]
  }
];

async function fun() {
await Promise.all(obj.map(async info => {
      console.log('info', JSON.stringify(info));
      await Promise.all(info.Address.map(async (items, index) => {
        console.log('ParentItems IsParentLossCapability',);
        let pr = await firstFunction();
        console.log('promise resolved: ' + pr)
        console.log('next step');
      }));
      console.log('UpdatedInfo', JSON.stringify(obj));
    }));
}
 async function firstFunction() {
  return new Promise((resolve, reject) => {
    let y = 0;
    setTimeout(() => {
      for (let i = 0; i < 10; i++) {
        y++;
      }
      console.log('loop completed');
      resolve(y);
    }, 2000);
  });
 }

fun();

我得到的输出如下，它说

1. info
2. info
3. loop completed
4. promise解决了
5. next step
6. UpdatedInfo
7. Loop completed
8. next step
9. UpdatedInfo

它应该能提供这样的输出，

1. info
2. loop completed
3. Promise解决方案: 10
4. next step
5. UpdatedInfo
6. info
7. loop completed
8. promise resolved: 10
9. next step
10. UpdatedInfo

Answer 1

当您使用.map(async (e) => {...})时，所有函数都会同时开始执行。await Promise.all(arr.map(async (e) => {...}))等待它们全部完成，但它仍然是并行的。

你想要的是按顺序排列。可以使用for循环：

for (let info of obj) {
      console.log('info', JSON.stringify(info));
      for (let index = 0 ; index < info.Address.length; index++) {
      let items = info.Address[index];
        console.log('ParentItems IsParentLossCapability',);
        let pr = await firstFunction();
        console.log('promise resolved: ' + pr)
        console.log('next step');
      }
      console.log('UpdatedInfo', JSON.stringify(obj));
}

或者使用异步缩减：

await obj.reduce(async (memo, info) => {
      await memo;
      console.log('info', JSON.stringify(info));
      await info.Address.reduce(async (memo2, items, index) => {
        await memo2;
        console.log('ParentItems IsParentLossCapability',);
        let pr = await firstFunction();
        console.log('promise resolved: ' + pr)
        console.log('next step');
      }), Promise.resolve());
      console.log('UpdatedInfo', JSON.stringify(obj));
    }, Promise.resolve());