$("document").ready(function()
{
  $("#contact_form").submit(function()
  {
    var name = $("#name").val();
    var email = $("#email").val();
    
    if(name.length == 0) alert("Please enter your name.");
    else
    {
      if(email.length == 0) alert("Please enter your email address.");
      else
      {
        var ampersat = email.indexOf("@");
        var dot = email.lastIndexOf(".");

        // make sure the email address contains an @ and a . and that there is a . after the @
        if(ampersat < 0 || dot < 0 || ampersat > dot) alert("Please enter a valid email address.");
        else return true;
      }
    }
    return false;
  });
});