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....');