promise顺序执⾏的⼏种⽅法const p1 = new Promise(resolve => {
setTimeout(() => {
resolve(1)
}, 1000)
})
const p2 = new Promise(resolve => {
setTimeout(() => {
resolve(2)
}, 3000)
})
const p3 = new Promise(resolve => {
setTimeout(() => {
resolve(3)
}, 2000)
})
const p4 = new Promise(resolve => {
setTimeout(() => {
resolve(4)
}, 1500)
})
const ps = [p1, p2, p3, p4]
// ⽅式⼀，递归
const run = (p) => {
p.then((d) => {
console.log(d)
const nextP = ps[ps.findIndex(f => f === p) + 1]
if (nextP) {
run(nextP)
}
})
}
run(ps[0])
// ⽅式⼆，generator 函数，也是 co 库核⼼
const run = (gen) => {
const it = gen()
let ret = it.next()
function step () {
if (!ret.done) {
ret.value.then(d => {
console.log(d)
ret = it.next(d)
step()
})
}
}
step()
await和async使用方法}
run(function *() {
for (let p of ps) {
yield p
}
})
// ⽅式三，组成 then 链
const run = () => {
let p = solve()
ps.forEach(item => {
p = p.then(() => item).then(console.log)
})
}

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