Node.js-提供了四种形式的定时器

 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....');