/**
 * Validates the following fields in the form, if they exist:
 * * name field - value must be non-blank
 * * email field - value must pass validation as per emailCheck() in email_check.js
 * * comment field - value must be non-blank
 *
 * To suppress validation of any field, just pass in an empty string as the field's name in the parameter list.
 */
function checkNameEmailAndCommentFields(form, nameFieldName, emailFieldName, commentFieldName)
{
  if ((nameFieldName != "") && (form.elements[nameFieldName].value == ""))
  {
    alert("Please enter your name");
    form.elements[nameFieldName].focus();
    return false;
  }

  if ((emailFieldName != "") && !emailCheck(form.elements[emailFieldName].value))
  {
    form.elements[emailFieldName].focus();
    return false;
  }

  if ((commentFieldName != "") && (form.elements[commentFieldName].value == ""))
  {
    alert("Please enter a comment");
    form.elements[commentFieldName].focus();
    return false;
  }

  return true;
}

/* Convenience functions */

function checkNameAndEmailFields(form, nameFieldName, emailFieldName)
{
  return checkNameEmailAndCommentFields(form, nameFieldName, emailFieldName, "")
}

function checkEmailField(form, emailFieldName)
{
  return checkNameEmailAndCommentFields(form, "", emailFieldName, "")
}