function validateForm(form) {
  if (form.username.value == "") {
    alert("Please enter a username.");
    form.username.focus();
    return false;
  } else if (form.password.value == "") {
    alert('Please enter your password.');
    form.password.focus();
    return false;
  } else {
    return true;
  }
}

// assumes there is a form named 'login' on page
function loginFieldFocus () {
  form = document.forms['loginForm'];
  field = form.username;
  field.focus()
}