[DOM] et tester si un attribut existe

function testAttribute ( _elemName_, _attrName_ ){
   var elem = document.getElementById(_elemName_);
   var found = false;
   var i = 0;
   if ( elem != null && elem.attributes != null ){
        while ( !found && i < elem.attributes.length ){
           if ( elem.attributes[i].name == _attrName )
              found = true;
           else
              i++;
        }
   }

  if ( found )
     return elem.attributes[i].value;
  else
     return null;
}