Note：这个答案只是涵盖了之间的时间差异await系列中和Promise.all。请务必阅读@mikep 的全面答案，还涵盖了错误处理中更重要的差异.
为了这个答案的目的，我将使用一些示例方法：
-
res(ms)是一个函数，它需要整数毫秒并返回一个在这么多毫秒后解析的承诺。
-
rej(ms)是一个函数，它需要整数毫秒并返回一个在这么多毫秒后拒绝的承诺。
Calling res启动计时器。使用Promise.all等待一些延迟将在所有延迟完成后解决，但请记住它们同时执行：
Example #1
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 ${n} milliseconds`, Date.now() - start)
}, n)
})
}
const data = await Promise.all([res(3000), res(2000), res(1000)])
console.log(`Promise.all finished`, Date.now() - start)
}
example()
这意味着Promise.all3 秒后将使用内部 Promise 的数据进行解析。
But, Promise.all具有“快速失败”行为:
Example #2
const data = await Promise.all([res(3000), res(2000), rej(1000)])
// ^^^^^^^^^ ^^^^^^^^^ ^^^^^^^^^
// delay 1 delay 2 delay 3
//
// ms ------1---------2---------3
// =============================O delay 1
// ===================O delay 2
// =========X delay 3
//
// =========X Promise.all
async function example() {
const start = Date.now()
let i = 0
function res(n) {
const id = ++i
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve()
console.log(`res #${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 ${n} milliseconds`, Date.now() - start)
}, n)
})
}
try {
const data = await Promise.all([res(3000), res(2000), rej(1000)])
} catch (error) {
console.log(`Promise.all finished`, Date.now() - start)
}
}
example()
如果你使用async-await相反，您必须等待每个承诺依次解决，这可能效率不高：
Example #3
const delay1 = res(3000)
const delay2 = res(2000)
const delay3 = rej(1000)
const data1 = await delay1
const data2 = await delay2
const data3 = await delay3
// ms ------1---------2---------3
// =============================O delay 1
// ===================O delay 2
// =========X delay 3
//
// =============================X await
async function example() {
const start = Date.now()
let i = 0
function res(n) {
const id = ++i
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve()
console.log(`res #${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()
