詳解如何構(gòu)建Promise隊(duì)列實(shí)現(xiàn)異步函數(shù)順序執(zhí)行

// 異步函數(shù)a
var a = function () {
 return new Promise(function (resolve, reject) {
 setTimeout(function () {
 resolve('a')
 }, 1000)
 })
}

// 異步函數(shù)b
var b = function (data) {
 return new Promise(function (resolve, reject) {
 resolve(data + 'b')
 })
}

// 異步函數(shù)c
var c = function (data) {
 return new Promise(function (resolve, reject) {
 setTimeout(function () {
 resolve(data + 'c')
 }, 500)
 })
}

//鏈?zhǔn)秸{(diào)用
a()
 .then(function (data) {
 return b(data)
 })
 .then(function (data) {
 return c(data)
 })
 .then(function (data) {
 console.log(data)// abc
 })

// 構(gòu)建隊(duì)列
function queue(arr) {
 var sequence = Promise.resolve()
 arr.forEach(function (item) {
 sequence = sequence.then(item)
 })
 return sequence
}

// 執(zhí)行隊(duì)列
queue([a, b, c])
 .then(data => {
 console.log(data)// abc
 })

async function queue(arr) {
 let res = null
 for (let promise of arr) {
 res = await promise(res)
 }
 return await res
}
queue([a, b, c])
 .then(data => {
 console.log(data)// abc
 })