Analysis:
1. If you need to jump, you need to use the href attribute of the location object.
2. To count down to 5 seconds, you need to use the timer setInterval.
HTML:
<div id="msg"></div>
JavaScript:
window.onload=function(){
var div=document.getElementById("msg");
var time=5;
var timer=setInterval(function(){
if(time==0){
location.href="https://www.4s5.cn";
}else{
div.innerHTML="将在 "+time+" 秒后跳转";
time--;
}
},1000)
}