var email = /^[a-zA-Z]{1}([a-zA-Z0-9]?[\.\-\_]{0,1}[a-zA-Z0-9]+)*[@]{1}(([a-zA-Z0-9]+[\.]{1})+([a-zA-Z]+))$/;

var password = /^[a-zA-Z0-9_]+$/;

var username = /^[a-zA-Z0-9_ ]+$/;

var numeric = /^[0-9]+$/;

var city = /^[a-zA-Z]+$/;

function feed_user()
{
     if(document.getElementById('username').value == '');
     else
     {
         if(!document.getElementById('username').value.match(username))
         {
              alert('Invalid user name:  Only alphabet and underscore are allowed.');
              document.getElementById('username').value="";
         }
     }
}

function feed_email()
{
    if(document.getElementById('email1').value == '');
    else
    {
        //validation for email
        if(!document.getElementById('email1').value.match(email))
        {
            alert('Please enter valid email adress.');
            document.getElementById('email1').value='';
        }
    }
}
function feed_mobile()
{
    if(document.getElementById('mobile').value == '');
    else
    {
        //validation for email
        if(!document.getElementById('mobile').value.match(numeric))
        {
            alert('Please enter a valid 10 Digit Mobile Number.');
            document.getElementById('mobile').value='';
        }
    }
}
function validblank()
{
      if(document.getElementById('username').value == '' || document.getElementById('email1').value == '')
           alert("Please fill the required fields");
}