等待Promise.all内部的诺言完成后再解决

问题描述

我有一个Promise.all，它可以执行映射到数组输入上的异步函数（如果它不为null），然后将数据解析为先前定义的Promise：

I have a Promise.all that executes asynchronous functions mapped on an array input if it's not null and then resolve data to a previously defined Promise:

Promise.all((inputs || []).map(input => {
  return new Promise((resolve, reject) => {
    someAsyncFunc(input)
    .then(intermediateOutput => {
      someOtherAsyncFunc(intermediateOutput )
      .then(output => {
        return Promise.resolve(output )
      })
      .catch(reason=> {
        return Promise.reject(reason)
      })
    })
    .catch(reason => {
      return Promise.reject(reason);
    })
  })
  .then(outputs => {
    resolve(outputs)
  })
  .catch(reason => {
    reject(reason)
  })
}))

在someAsyncFunc完成工作之前，我只能得到空的输出。如何使Promise.all等待内部的诺言完成异步工作？

I only get empty outputs before even someAsyncFunc finishes its work. How can make Promise.all wait for the promises inside to finish their asynchronous work ?

推荐答案

请参阅jfriend的评论。

See jfriend's comment.

someAsyncFunc 和 someOtherAsyncFunc 是可以正确返回promise
的函数，例如 return new Promise（/ *。 .. * /）;

someAsyncFunc and someOtherAsyncFunc are function that properly return a promisewith something like return new Promise(/*...*/);

这没用：

.then(output => {
  return Promise.resolve(output )
})

阅读Promise文档

read the Promise documentation

相同

.catch(reason=> {
  return Promise.reject(reason)
})

该承诺已经被拒绝，您不需要捉住并拒绝自己

the Promise is already rejecting, you don't need to catch and reject yourself

确保承诺是可链接的，您需要返回承诺

to make sure Promises are chainable you need to return the Promise

// ...
return new Promise((resolve, reject) => {
  if(inputs == null)
    resolve([]);
  else {
    Promise.all(inputs.map(input => {
      return someAsyncFunc(input)
        .then(someOtherAsyncFunc)
    }))
      .then(resolve)
      .catch(reject)
  }
});

请注意，我宁愿不要为Promise做麻烦，因为它们全部是内联的，它增加了视觉上的混乱： p>

note I would rather not make the arry for Promise.all inline, it adds visual clutter:

return new Promise((resolve, reject) => {
  if(inputs == null)
    resolve([]);
  else {
    const myPromises = inputs.map(input => {
      return someAsyncFunc(input)
        .then(someOtherAsyncFunc)
    });
    Promise.all(myPromises)
      .then(resolve)
      .catch(reject)
  }
});

如果您犯了其他错误，它可能仍然会失败。

it may still fail if you made other mistakes.

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