ecmascript changequery

<script type="text/javascript">
 var groupscollection=document.getElementById("groups");
var clientContext = null;
var web = null;
var allUserAndGroup = new Array();
var bol = new Boolean(false);
ExecuteOrDelayUntilScriptLoaded(Initialize, "sp.js");
function Initialize()
{
clientContext = new SP.ClientContext.get_current();
web = clientContext.get_web();
this.site = clientContext.get_site();
                                              
clientContext.load(site);
clientContext.executeQueryAsync(Function.createDelegate(this, this.onSiteQuerySucceeded1), Function.createDelegate(this, this.onSiteQueryFailed));
}          
function onSiteQuerySucceeded1(sender, args) {              
          clientContext = SP.ClientContext.get_current();  
          var changequery = new SP.ChangeQuery(false,false);
          var starttimetoken = new SP.ChangeToken();
          starttimetoken.set_stringValue("1;1;"+site.get_id().ToSerialized()+";634135418586210924;-1");
          var endtimetoken = new SP.ChangeToken();
          endtimetoken.set_stringValue("1;1;"+site.get_id().ToSerialized()+";634135436586210924;-1");
          changequery.set_changeTokenStart(starttimetoken);
          changequery.set_changeTokenEnd(endtimetoken);
          changequery.set_group(true);
          changequery.set_groupMembershipAdd(true);
          changequery.set_groupMembershipDelete(true);      
          this.changes = site.getChanges(changequery);
          clientContext.load(changes);
          clientContext.executeQueryAsync(Function.createDelegate(this, this.onSiteQuerySucceeded), Function.createDelegate(this, this.onSiteQueryFailed));
}

function onSiteQuerySucceeded(sender, args) {
    debugger;              
       alert(this.changes.get_count());       
}     

function onSiteQueryFailed(sender, args) {
 alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}