串行等待请求在并行运行的返回中? [英] serial await requests in a return run in parallel?

问题描述

与某人进行讨论并遇到了这种奇怪情况:

Having a discussion with someone and came across this oddity:

const wait = async () => new Promise(resolve => setTimeout(resolve, 1000));

async function case1() {
  const {a, b} = {a: await wait(), b: await wait()};
  return {a, b};
}

async function case2() {
  return {a: await wait(), b: await wait()};
}

async function case3() {
  const {a, b} = {a: wait(), b: wait()};
  return {a: await a, b: await b};
}

async function case4() {
  const {a, b} = {a: wait(), b: wait()};
  const {c, d} = {c: await a, d: await b};
  return {c, d};
}

function test() {
  const start = new Date();

  case1().then(() => console.log('case1:', +new Date() - start));
  case2().then(() => console.log('case2:', +new Date() - start));
  case3().then(() => console.log('case3:', +new Date() - start));
  case4().then(() => console.log('case4:', +new Date() - start));
}

case1和case2都在2秒内运行. case3和case4在1秒钟内运行.

case1 and case2 both run in 2 seconds. case3 and case4 run in 1 second.

是否存在一些奇怪的隐式Promise.all或其他内容?

Is there some weird implicit Promise.all or something??

推荐答案

在不使用case3和case4处的await的情况下调用函数wait().就是这样.

You call the function wait() without utilizing await at case3 and case4. That is the difference.

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