Validation of Url

function validateUrl()
{
obj=document.getElementById(‘txtUrl’);
msg=”Enter valid url”;
var urlStr = /^\http\:\/\/[a-zA-Z]{3,}\.[a-zA-Z0-9]{2,}
(\.[a-zA-Z]{2,3}|\.[a-zA-Z]{2,3}\.[a-zA-Z]{2})$/;
if (urlStr.test(obj.value) == false)
{
alert(msg);
obj.focus();
obj.select();
return false;
}
return true;
}