js 3秒后跳转页面

<script>
  var i = 4;
  function out(){
    if (i>0){
      i--;
    }else{
      location.href="跳转的地址";
    }
    document.getElementById('aa').innerHTML=i;
  }
  setInterval('out()',1000);
</script>
<div id="aa"></div>