node中IO以及定时器优先级详解

console.log("step one")
setTimeout(function(){
  console.log("settimeout2")
 },0)
 setInterval(function(){
   console.log("timeInterval")
 },1000)
let sum=0;
for(let i=0;i<=100000;i++){
  for(let j=0;j<=100000;j++){
    sum+=i*j
  }
}
console.log("setp two",sum)

执行结果
sogubaby ~/Desktop/learn_node/manyprocess$node sync.js 
step one
setp two 25000500002539570000
settimeout2
timeInterval
timeInterval
timeInterval
timeInterval

会发现，当前循环已经阻塞了Tick的执行，所以定时器被延误了

console.log("step one")
setImmediate(function(){
  console.log("setInmediate")
})
let sum=0;
for(let i=0;i<=1000000;i++){
  for(let j=0;j<=100000;j++){
    sum+=i*j
  }
}
console.log("setp two",sum)

执行结果如下
sogubaby ~/Desktop/learn_node/manyprocess$node sync.js 
step one
setp two 2.500027500029909e+21
setInmediate

说明主线程会阻塞的，当前线程执行完后，才会进入到下一个循环

process.nextTick(function(){
  console.log("process.nextTick")
})
setImmediate(function(){
  console.log("setImmediate")
})
setTimeout(function(){
 console.log("setTimeout")
},0)
let sum=0;
console.log("setp two",sum)

执行结果
setp two 0
process.nextTick
setTimeout
setImmediate