JS 获取地址栏三级域名

<script type="text/javascript"> 

function Char(str) {
  var uchars = {};
  str.replace(/\S/g, function (l) {
    uchars[l] = (isNaN(uchars[l])) ?  : uchars[l] +
  })
  return uchars
}
var host = window.location.host;
var count = Char(host);
    if(count["."] == ){
        str = str.split(".")[];
        //str = str.split("//")[1];
        console.log(str);
    }else{
        console.log("fuck you");
    }
</script>