javascript 转换数字千分符

var $=function(){
return document.getElementById(arguments[0]);
}
function get(){
var val=$('val').value;
if(val!=''&&!isNaN(val)){
re=/(\d{1,3})(?=(\d{3})+(?:$|\.))/g;
n=val.replace(re,"$1,");
alert(n);
}
else alert('请输入数字');
}