2018.7.30

一次性定时器：setTimeout

清除一次性定时器用clearTimeout

var timer=setTimeout(show,3000);
btn1.onclick=function(){
    clearTimeout(timer);
}

永久性定时器：setInterval

清除永久性定时器用clearInterval

var times=setInterval(print,1000);
btn2.onclick=function(){
  clearInterval(times);
}