JavaScript如何处理并行请求？四种方式浅析(2)-木庄网络博客

generator使用co函数

const co = require('co')
const startTime = new Date().getTime()
function request (time) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(time)
    }, time)
  })
}
co(function* () {
  let request1 = request(3000);
  let request2 = request(2000);
  let res1 = yield request1
  let res2 = yield request2
  console.log(res1, res2, new Date() - startTime) // 3000 2000 3001
})

有了co函数，就不需要生成it和执行next方法了； co的原理其实也简单，就是递归执行next，直到done为true；如果next返回的value是Promise，则在then函数中执行next，若不是Promise，直接执行next函数下面是co函数的简版手写实现

function co(func) {
  let it = func()
  let t = it.next()
  next()
   
  function next() {
    if (t.done) return
    if (t.value instanceof Promise) {
      t.value.then(res => {
        t = it.next(res)
        next()
      })
    } else {
      t = it.next(t.value)
      next()
    }
  }
}

方法四

有了generator，很容易想到async/await，毕竟async/await就是由generator实现的

// setTimeout模拟异步请求，time为请求耗时
const startTime = new Date().getTime()
function request (time) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve(time)
    }, time)
  })
}
(async function () {
  let request1 = request(3000)
  let request2 = request(2000)
  let res1 = await request1
  console.log(res1, new Date() - startTime) // 3000 3001
  let res2 = await request2
  console.log(res2, new Date() - startTime) // 2000 3005
})()