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

问题描述

似乎在将 async/await 与 .reduce() 合并时遇到了一些问题，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 对象在 this.store 完成之前被记录...

The data object is logged before the this.store completes...

我知道您可以将 Promise.all 与异步循环一起使用，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

问题是您的累加器值是承诺 - 它们是 async function 的返回值.要获得顺序评估(以及所有等待的最后一次迭代)，您需要使用

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(…));

也就是说，对于async/await，我通常会推荐使用普通循环代替数组迭代方法，它们的性能更高且通常更简单.

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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