串行Promise

[vaakian]

Promise.all是并行的，此处3种方法实现串行Promise

function f1() {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve('A')
        }, 300)
    })
}
function f2() {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve('B')
        }, 100)
    })
}
function f3() {
    return new Promise((resolve) => {
        setTimeout(() => {
            resolve('C')
        }, 110)
    })
}

// 1. 递归法，最简单
function serialPromise1(promises = [], i = 0) {
    promises[i]().then(data => {
        console.log(data)
        i + 1 < promises.length && serialPromise2(promises, i + 1)
    })
}
// 2. 语法糖迭代法
async function serialPromise2(promises = []) {
    for (let i = 0; i < promises.length; ++i) {
        let res = await promises[i]()
        console.log(res)
    }
}
// 3. 抛去语法糖外衣的迭代法
const serialPromise3 = function (promises = []) {
    // promises.reduce((prev, next, i) => {
    //     return prev.then(next).then(data => console.log({ data, i }))
    // }, Promise.resolve());
    let p = Promise.resolve()
    for (let i = 0; i < promises.length; ++i) {
        p = p.then(promises[i])
        p.then(data => console.log(data))
    }
}

serialPromise3([f1, f2, f3])