JS ：3秒后自动跳转功能

function jump(){

window.location.href='1.html';
}
setTimeout(jump, 3000);

<span id="cnt">4</span>秒钟后将自动跳转到首页...
<script>
var counter = 3;
var timer1 = null;
function jump(){
if(counter>=0){
document.getElementById('cnt').innerHTML = counter;
counter--;
}else{
clearInterval(timer1);
location.href='1.html';
}
}
timer1 = setInterval(jump, 1000);

</script>