var httpRequest = false;  //Instanz des XML-HTTP-Objekts
var noResult = "Kein Ergebnis"; // Text, der ausgegeben werden soll, wenn eine Ajax-Operation keine Daten vom Server erhält.

function doHttpRequest(url, paramStr, fieldId) {
	httpRequest = false;
   
   	if(window.XMLHttpRequest)  // Mozilla, Safari,...
       		httpRequest = new XMLHttpRequest();
  	 else if(window.ActiveXObject) { // IE
       		try {
           		httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
    		}
       		catch (e) {
           		try {
              			httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
     			}
          		 catch (e) {}
       		}
   	}
   
   	if(!httpRequest) 
      		return false;
      
	httpRequest.onreadystatechange = function() {
      		if(httpRequest.readyState == 4) {
         		if(httpRequest.status == 200)
            			handleHttpResponse(httpRequest.responseText, fieldId);
        			else
          			return false;
         		}
    		else
       			return false;
   		} 
   httpRequest.open('post', url, true);
   httpRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded; charset=iso-8859-1")
   
   httpRequest.send(paramStr);
}

function handleHttpResponse(content, fieldId) {
	outputId = fieldId + '_msg';
	if(!document.getElementById)
      		return false;
   	if(!document.getElementById(outputId))
   		return false;
   	if(content == false) { // "FALSE"
      		document.getElementById(fieldId).style.background = '#F3F2ED';
      		document.getElementById(outputId).innerHTML = noResult;
      		document.getElementById(outputId).style.display = 'none';
      		/* document.getElementById(outputId).style.visibility = 'none'; */
      	}
   	else	{
      		document.getElementById(outputId).innerHTML = content;
      		document.getElementById(outputId).style.display = 'block';
      		/* document.getElementById(outputId).style.visibility = 'visible'; */
      		document.getElementById(outputId).style.color = '#666666';
      		document.getElementById(fieldId).style.background = '#f2ce4d';
      	}
} 

function checkConstraint(fieldObject) {
	scriptUrl = "/forms/constraints.php";
	paramStr = encodeURIComponent(fieldObject.name)+'='+encodeURIComponent(fieldObject.value);
	doHttpRequest(scriptUrl, paramStr, fieldObject.id);
}