等待Promise.all（）和多个等待之间的任何区别？

问题描述：

之间有什么区别：

const [result1, result2] = await Promise.all([task1(), task2()]);

和

const t1 = task1();
const t2 = task2();

const result1 = await t1;
const result2 = await t2;

和

const [t1, t2] = [task1(), task2()];
const [result1, result2] = [await t1, await t2];

答

出于本回答的目的，我将使用一些示例方法：

For the purposes of this answer I will be using some example methods:

res（ms）是一个取整数的函数毫秒并返回一个在很多毫秒后解析的promise。

rej（ms）是一个需要整数毫秒的函数返回一个在很多毫秒后拒绝的承诺。

res(ms) is a function that takes an integer of milliseconds and returns a promise that resolves after that many milliseconds.
rej(ms) is a function that takes an integer of milliseconds and returns a promise that rejects after that many milliseconds.

调用 res 启动计时器。在所有延迟完成后，使用 Promise.all 等待一些延迟将解决，但请记住它们同时执行：

Calling res starts the timer. Using Promise.all to wait for a handful of delays will resolve after all the delays have finished, but remember they execute at the same time:

const data = await Promise.all([res(3000), res(2000), res(1000)])
//                              ^^^^^^^^^  ^^^^^^^^^  ^^^^^^^^^
//                               delay 1    delay 2    delay 3
//
// ms ------1---------2---------3
// =============================O delay 1
// ===================O           delay 2
// =========O                     delay 3
//
// =============================O Promise.all

async function example() {
  const start = Date.now()
  let i = 0
  function res(n) {
    const id = ++i
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve()
        console.log(`res #${id} called after ${n} milliseconds`, Date.now() - start)
      }, n)
    })
  }

  const data = await Promise.all([res(3000), res(2000), res(1000)])
  console.log(`Promise.all finished`, Date.now() - start)
}

example()

这意味着 Promise.all 将在3秒后解决内部承诺中的数据。

This means that Promise.all will resolve with the data from the inner promises after 3 seconds.

但是， Promise.all 有快速失败行为：

But, Promise.all has a "fail fast" behavior:

const data = await Promise.all([res(3000), res(2000), rej(1000)])
//                              ^^^^^^^^^  ^^^^^^^^^  ^^^^^^^^^
//                               delay 1    delay 2    delay 3
//
// ms ------1---------2---------3
// =============================O delay 1
// ===================O           delay 2
// =========X                     delay 3
//
// =========X                     Promise.all

async function example() {
  const start = Date.now()
  let i = 0
  function res(n) {
    const id = ++i
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve()
        console.log(`res #${id} called after ${n} milliseconds`, Date.now() - start)
      }, n)
    })
  }
  
  function rej(n) {
    const id = ++i
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        reject()
        console.log(`rej #${id} called after ${n} milliseconds`, Date.now() - start)
      }, n)
    })
  }
  
  try {
    const data = await Promise.all([res(3000), res(2000), rej(1000)])
  } catch (error) {
    console.log(`Promise.all finished`, Date.now() - start)
  }
}

example()

如果您使用 async-await ，则必须等待每个承诺按顺序解析，这可能不是高效：

If you use async-await instead, you will have to wait for each promise to resolve sequentially, which may not be as efficient:

const delay1 = res(3000)
const delay2 = res(2000)
const delay3 = rej(1000)

const data1 = await delay1
const data2 = await delay2
const data3 = await delay3

// ms ------1---------2---------3
// =============================O delay 1
// ===================O           delay 2
// =========X                     delay 3
//
// =============================X await

async function example() {
  const start = Date.now()
  let i = 0
  function res(n) {
    const id = ++i
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve()
        console.log(`res #${id} called after ${n} milliseconds`, Date.now() - start)
      }, n)
    })
  }
  
  function rej(n) {
    const id = ++i
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        reject()
        console.log(`rej #${id} called after ${n} milliseconds`, Date.now() - start)
      }, n)
    })
  }
  
  try {
    const delay1 = res(3000)
    const delay2 = res(2000)
    const delay3 = rej(1000)

    const data1 = await delay1
    const data2 = await delay2
    const data3 = await delay3
  } catch (error) {
    console.log(`await finished`, Date.now() - start)
  }
}

example()

等待Promise.all（）和多个等待之间的任何区别？

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