Das einfachste und stabilste Ajax-Objekt für alle Browser. Für Alle die gern selbst programmieren und auf jquery oder mootools verzichten wollen, eine sehr interessante Alternative:

  // Ajax Object - cns version 2011  
  function ajaxObject(url, callbackFunction) {  
    var me=this;  
    this.updating = false;  
    this.abort = function() {  
      if (me.updating) {  
        me.updating=false;  
        me.AJAX.abort();  
        me.AJAX=null;  
      }  
    };  
    this.update =  
    function(passData,postMethod) {  
      if (me.updating) { return false; }  
      me.AJAX = null;  
      if (window.XMLHttpRequest) {  
        me.AJAX=new XMLHttpRequest();  
      }else{  
        me.AJAX=new ActiveXObject("Microsoft.XMLHTTP");  
      }  
      if (me.AJAX==null) {  
        return false;  
      }else{  
        me.AJAX.onreadystatechange = function() {  
          if (me.AJAX.readyState==4) {  
            me.updating=false;  
            me.callback( me.AJAX.responseText, me.AJAX.status, me.AJAX.responseXML,  me.AJAX.getAllResponseHeaders() );  
            me.AJAX=null;  
          }  
        };  
        me.updating = new Date();  
        if (/post/i.test(postMethod)) {  
          var uri=urlCall+(/\?/i.test(urlCall)?'&':'?')+'timestamp='+me.updating.getTime();  
          me.AJAX.open("POST", uri, true);  
          me.AJAX.setRequestHeader("Content-type", "application/x-www-form-urlencoded");  
          me.AJAX.setRequestHeader("Content-Length", passData.length);  
          me.AJAX.send(passData);  
        }else{  
          var uri=urlCall+(/\?/i.test(urlCall)?'&':'?')+passData+'&timestamp='+(me.updating.getTime());  
          me.AJAX.open("GET", uri, true);  
          me.AJAX.send(null);  
        }  
        return true;  
      }  
    };  
    var urlCall = url;  
    this.callback = callbackFunction || function (){};  
  }

// Formular auslesen und zu AjaxPostData zusammenfügen
function getAjaxFormData( form, data ){
  data = data || "";
  for(i=0; i<form.elements.length; i++){
    el = form.elements[i];
    if(el.type!=null) switch(el.type.toLowerCase()){
      case "hidden":  
      case "text":  
      case "password":  
      case "textarea": 
      case "button": 
        data += "&" + el.name + "=" + encodeURIComponent(el.value);
      break;
      case "radio":
      case "checkbox": 
        data += (el.checked ? "&" + el.name + "=" + encodeURIComponent(el.value) : ""); 
      break;
      case "select":
      case "select-one": if(el.options.length>0) data += "&" + el.name + "=" + encodeURIComponent(el.options[el.selectedIndex].value); break;
      // TODO multiselect auswerten
    } 
  }
  return data;
}

// Formular per Ajax senden
function sendAjaxForm( form ){       
  data = getAjaxFormData(form);   
  AXSendForm = new ajaxObject("?action=save", callBackFunc );   
  AXSendForm.update(data,"post");   
  return false;   
}