function isEmail(email) {
  var reg1 = /(@.*@)|(\.\.)|(@\.)|(\.@)|(^\.)/;                               // not valid
  var reg2 = /^.+\@(\[?)[a-zA-Z0-9\-\.]+\.([a-zA-Z]{2,4}|[0-9]{1,4})(\]?)$/; // valid

  return (!reg1.test(email) && reg2.test(email));
}


function ValidateForm(frm) {

  var isError = false;
  var errorMessage = "";
  
   if(frm.first_name.value == "") {
    isError = true;
    errorMessage += '\nMissing First Name';
  }

  if(frm.last_name.value == "") {
    isError = true;
    errorMessage += '\nMissing Last Name';
  }

  if(frm.email.value == '') {
    isError = true;
    frm.email.focus();
    errorMessage += '\nMissing Email';
  } else {
    if(!isEmail(frm.email.value)) {
    isError = true;
    frm.email.focus();
    errorMessage += 'Invalid Email!';
    }
  }
  
  if(frm.phone.value == "") {
    isError = true;
    errorMessage +='\nMissing Phone ';
  }

  if(isError == true) {
    alert('Missing required fields:\n' + errorMessage);
    return false;
  }

  return true;
}