Meine lightweight Ajax-Klasse

function test_interval( interval )
{
	var ajaxTimer = new msAjax();
	ajaxTimer.set( ajaxTimer.config, "interval", interval );

	ajaxTimer.intervalSend(
		ajaxTimer,
		'timer_test',
		function( retval ){
			$('#test-interval').html( retval );
		}
	);
}

function test_timer( timeout )
{
	var ajaxTimer = new msAjax();
	ajaxTimer.set( ajaxTimer.config, "timer", timeout );

	ajaxTimer.timerSend(
		ajaxTimer,
		'timer_test',
		function( retval ){
			$('#test-timer').html( retval );
		}
	);
}

/* 
 * Distributed under the terms of the GPL:
 * Copyright (c) 2009, Matthias Sonnenkalb
 * (www.matthias-sonnenkalb.net, msonnenkalb@gmx.de)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * 
 */

function msAjax(){

   var xhr = false;

   this.config = {
      'URL' : 'http://',
      'widgetBase' : 'widgets.inc.php',
      'asynchronous' : true,
      'method' : 'POST',
      'charset' : 'UTF-8',
      'cache' : false,
      'timer' : 0,
      'interval' : 0,
      'headers' : {
      'X-Requested-With' : 'XMLHttpRequest',
      'X-MsAjax-Version' : '1.2',
      'Accept' : 'text/javascript, text/html, application/xml, text/xml, */*',
      'Content-Type' : 'application/x-www-form-urlencoded; charset=UTF-8'
	}
   };

   /**
    * send.
    *
    * send request (try to get the widget).
    */
   this.send = function( widgetName, callbackFunc, argsObj ) {
      if( xhr ) {
         xhr.open( this.config.method, this.config.URL + 
                   this.config.widgetBase, this.config.asynchronous );

         if( this.config.asynchronous == true ) {
            xhr.onreadystatechange = function() {
               if( xhr.readyState == 4 ) {
                  try {
                     retval = JSON.parse( unescape( xhr.responseText ));
                     if( !!callbackFunc ) {
                        callbackFunc( retval );
                     }
                  }catch( e ){
                     alert("invalid server response");
                  }
               }
            };
         }

         for( var header in this.config.headers ) {
            xhr.setRequestHeader( header, this.config.headers[header] );
         }

         xhr.send( data( widgetName, argsObj ));

         if( this.config.asynchronous == false ) {
            try {
               retval = JSON.parse( unescape( xhr.responseText ));
               if( !!callbackFunc ) {
                  callbackFunc( retval );
               }
            }catch( e ){
               alert("invalid server response");
            }
         }
      }
   }

   /**
    * timerSend.
    *
    * will be called once if timerout (config.timer) is reached.
    */
   this.timerSend = function( objInstance, widgetName, callbackFunc, argsObj ) {
      setTimeout( function(){
         objInstance.send( widgetName, callbackFunc, argsObj );
      }, objInstance.config.timer );
   }

   /**
    * intervalSend.
    *
    * will be called every n-milliseconds (n is defined by value of config.interval).
    */
   this.intervalSend = function( objInstance, widgetName, callbackFunc, argsObj ) {
      setInterval( function(){
         objInstance.send( widgetName, callbackFunc, argsObj );
      }, objInstance.config.interval );
      this.send( widgetName, callbackFunc, argsObj );
   }

   /**
    * set.
    *
    * configuration setter.
    */
   this.set = function( obj, prop, value ){
      obj[prop] = value;
   }

   /**
    * set.
    *
    * configuration getter.
    * returns 'undefined' if propterty not available
    */
   this.get = function( obj, prop ){
      return obj[prop];
   }

   /**
    * toString.
    *
    * provides the configuration object as a string.
    */
   this.toString = function( obj ){
      var str = "{\n";

      for( var prop in obj ){
         if( typeof obj[prop] == "object" ) {
            str += prop + " : " + this.toString( obj[prop] );
         }else{
            str += prop + " = " + obj[prop] + "\n";
         }
      }

      return str + "}\n";
   }

   /**
    * build up a request object
    *
    * widgetName (string) - name of widget we want to request
    * argsObj (json-object) - parameter given to widget (optional)
    *
    * return boolean true or false
    */
   var data = function( widgetName, argsObj ){
      if( !widgetName ){
         alert('no widget-name given');
         return false;
      }

      var data = new Object();
      data.widgetName = widgetName;

      if( argsObj ){
         data.argsObj = new Object();
         for( var property in argsObj ){ 
            if( argsObj[property] != null && typeof argsObj[property] != 'object' ){
               data.argsObj[property] = encodeURIComponent( argsObj[property] );
            }else{
               data.argsObj[property] = argsObj[property];
            }
         }
      } else {
         data.argsObj = null;
      }

      return 'args=' + escape( JSON.stringify( data ));
   }

   // -------------------------------------------------------
   // try to get an request instance
   // -------------------------------------------------------
   // Mozilla, Opera, Safari and IE (>= v7)
   if( window.XMLHttpRequest ){
      xhr = new XMLHttpRequest();
   // IE 6 or prior
   }else{
      try {
         xhr = new ActiveXObject("Msxml2.XMLHTTP");
      }catch( e ){
         try {
            xhr = new ActiveXObject("Microsoft.XMLHTTP");
         }catch( e ){
            alert("cannot get an instance of XMLHttpRequest object");
            xhr = false;
         }
      }
   }
}