function ff_alternate_rows(id){
//alert(id);
//http://articles.sitepoint.com/article/background-colors-javascript
 if(document.getElementsByTagName){
   var table = document.getElementById(id);
   var rows = table.getElementsByTagName("tr");
   for(i = 0; i < rows.length; i++){//manipulate rows
     if(i % 2 == 0){
       rows[i].className = "ffgroen";
     }else{
       rows[i].className = "ffgray";
     }
   }
 }
}

function getElementsByClassName(className, tag, elm){
   var testClass = new RegExp("(^|\\s)" + className + "(\\s|$)");
   var tag = tag || "*";
   var elm = elm || document;
   var elements = (tag == "*" && elm.all)? elm.all : elm.getElementsByTagName(tag);
   var returnElements = [];
   var current;
   var length = elements.length;
   for(var i=0; i<length; i++){
       current = elements[i];
       //alert(current.style.)
       //alert(testClass.test(current.id));
       if(testClass.test(current.className)){
           returnElements.push(current);
       }
   }
   return returnElements;
}


function vac_alternating_rows() {
  var vacatures = getElementsByClassName('vacancy', 'div', document);
  aantal = vacatures.length;
  for(var i=0; i<aantal; i++){
     //vac = vacatures[i];
     if(i % 2 == 0){
       vacatures[i].className = "vac_groen";
     }else{
       vacatures[i].className = "vac_gray";
     }
  }
}