异步并发

const fs = require('fs')

let out = after(2,()=>{
    console.log(renderObj)
})
const after = (times,fn)=>()=>--times == 0 && fn()

let renderObj = {}
fs.readFile('./name.txt','utf-8',function(err,data){
    renderObj.name = data;
    out()
})

fs.readFile('./age.txt','utf-8',function(err,data){
    renderObj.age = data
    out()
})

核心是通过计数来保证同时获取多个并发的完整数据    类似的方法还有promise.all()