javascript - 在解决之前等待 Promise.all 中的 promise 完成

Question

我有一个 Promise.all，如果它不为空，它会执行映射到数组输入上的异步函数，然后将数据解析为先前定义的 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 完成其工作之前，我只得到空输出。如何让 Promise.all 等待里面的 promise 完成他们的异步工作？

Answer 1

不只是

return Promise.all((inputs || []).map(input =>
 somePromiseFunc(input).then(someOtherPromiseFunc)
);

工作？

你不是第一次使用 Promise.all ，因为它需要一个 promise 数组作为输入，而不是 (resolve, reject) => { ... }/

Promise.all 将在其中一个底层 promise 失败后立即被拒绝，因此您无需尝试围绕 catch(error => reject(错误)

例子:

const somePromiseFunc = (input) => new Promise((resolve, reject) => {
  setTimeout(() => {
    if (input === 0) { reject(new Error('input is 0')); }
    resolve(input + 1);
  }, 1000);
});

const someOtherPromiseFunc = (intermediateOutput) => new Promise((resolve, reject) => {
  setTimeout(() => {
    if (intermediateOutput === 0) { reject(new Error('intermediateOutput is 0')); }
    resolve(intermediateOutput + 1);
  }, 1000);
});

const f = inputs => {
  const t0 = Date.now()
  return Promise.all((inputs || []).map(input => somePromiseFunc(input).then(someOtherPromiseFunc)))
    .then(res => console.log(`result: ${JSON.stringify(res)} (after ${Date.now() - t0}ms)`))
    .catch(e => console.log(`error: ${e} (after ${Date.now() - t0}ms)`));
};

f(null)
// result: [] (after 0ms)

f([1, 0])
// error: Error: input is 0 (after 1001ms)

f([1, -1])
// error: Error: intermediateOutput is 0 (after 2002ms)

f([1, 2])
// result: [3,4] (after 2002ms)