JavaScript数组.reduce与async / await [英] JavaScript array .reduce with async/await

问题描述

似乎有一些问题将async / await与.reduce（）结合起来，如下所示：

Seem to be having some issues incorporating async/await with .reduce(), like so:

const data = await bodies.reduce(async(accum, current, index) => {
  const methodName = methods[index]
  const method = this[methodName]
  if (methodName == 'foo') {
    current.cover = await this.store(current.cover, id)
    console.log(current)
    return {
      ...accum,
      ...current
    }
  }
  return {
    ...accum,
    ...method(current.data)
  }
}, {})
console.log(data)

data <$ em>

我知道你可以利用 Promise.all 使用异步循环，但这是否适用于 .reduce（）？

I know you can utilise Promise.all with async loops, but does that apply to .reduce()?

推荐答案

问题是你的累加器值是承诺 - 它们的返回值是 async functi上秒。为了获得顺序评估（除了最后一次迭代之外的所有迭代），你需要使用

The problem is that your accumulator values are promises - they're return values of async functions. To get sequential evaluation (and all but the last iteration to be awaited at all), you need to use

const data = await array.reduce(async (accumP, current, index) => {
  const accum = await accumP;
  …
}, Promise.resolve(…));

这就是说， async / await 我一般建议使用普通循环代替数组迭代方法 ，它们的性能更高，而且更简单。

That said, for async/await I would in general recommend to use plain loops instead of array iteration methods, they're more performant and often simpler.

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