function isNotEmpty(elem_id) {
        var str=document.getElementById(elem_id).value;
        var re = /.+/;

        if(!str.match(re)) {
           showErrorMsg(elem_id);
           return false;
        }else{
           hideErrorMsg(elem_id);
           return true;
        }
    }

    function showErrorMsg(elem_id) {
      var err_str = 'err_' + elem_id;
      document.getElementById(err_str).style.display = 'block';
    }

    function hideErrorMsg(elem_id) {
      var err_str = 'err_' + elem_id;
      document.getElementById(err_str).style.display = 'none';
    }

    function validateForm(formName)
    {
       var true_counter = 0;
       if(isNotEmpty('email')){ true_counter++; }
       if(isNotEmpty('name')){ true_counter++; }
       if(isNotEmpty('sername')){ true_counter++; }
       if(isNotEmpty('text')){ true_counter++; }

       if(true_counter == 4) {
            return true;
       }else{
            return false;
       }
    }