Node.js提供了四种形式的定时器

 global.setTimeout();      //一次性定时器

 global.setInterval();       //周期性定时器

 global.nextTick();          //本次事件循环结束时立即执行的定时器

 global.setImmediate();  //下次事件循环立即执行的定时器

 var i=1;

 setTimeout(()=>{

     console.log(i);

 },1000);

 //1秒之后，打印出0，1,2,3,4

 for(var i=1;i<=3;i++){

     setTimeout(()=>{

         console.log(i)

     },1000)

 }

 //闭包

 for(var i=1; i<=3; i++){

     setTimeout(outer(i),1000)  //定期定时器

 }

 function outer(num){

     return function(){

         console.log(num)

     };

 }

 //使用箭头函数完成上面的闭包功能

 for(var i=1;i<=3;i++){

     setTimeout(((num)=>{

         return ()=>{console.log(num);}})(i),1000)

 }

 setInterval 周期性定时器

 var count=0;

 var timer=setInterval(function(){

     count++;

     console.log('%d hello',count);

     if(count>5){

         clearInterval(timer);

     }

   },1000);

 //setTimeout  一次性定时器

 var count2=0;

 var timer2=setTimeout(function(){

     count2++;

     if(count2<=5){

         console.log('%d hello',count2);

         setTimeout(arguments.callee,1000);  //arguments

     }else{

         clearTimeout(timer2);

     }

 },1000)

 //setImmediate(); 下次事件循环立即执行的定时器

 setImmediate(function(){

     console.log('Immediate 1.....');

 });

 process.nextTick(function(){

     console.log('nextTick 1......');

 });

 setTimeout(function(){console.log('setTimeout 2....')},1000)

 process.nextTick(function(){

     console.log('nextTick 2......');

 });

 setImmediate(function(){

     console.log('nextTick 3......');

 });

 console.log('end....');