window.onload = addHandler;

function addHandler(){
 var required = Array("enquiryform_name","enquiryform_telephone","enquiryform_email","enquiryform_query");
 var errors;
 var submitbutton = document.getElementById("submit");
  
submitbutton.onclick=function(){
  errors = checkForm(required);
  if(errors.length < 1 )
  {
   return;
  } else {
   markErrors(errors);
   alert("Please make sure all mandatory fields are complete!");return false;
  }
 }
}
function markErrors(ef)
{
 for(var i=0;i<document.getElementsByTagName('label').length;i++)
 {
  document.getElementsByTagName('label')[i].setAttribute("class","");
  for(var j=0;j<ef.length;j++) {
   if(document.getElementsByTagName('label')[i].htmlFor==ef[j].id)
   {
    document.getElementsByTagName('label')[i].setAttribute("class","error");
   }
  }
 }
}
function checkForm(cf)
{
 var errors = Array();
 for(var i = 0; i < cf.length; i++)
 {
  var rElement = document.getElementById(cf[i]);
  if(rElement.value == ""){errors.push(rElement);}
 }
 return errors;
}