in the mootools

 
         if('identity'){
        	 $('identity').addEvent('change',function(event){
        		 new Event(event).stop();
        		 var requrl=getCurrentAppLocation()+"/chidentity.do";
        		 new Ajax(requrl,{
        			 method:'get',
        			 data:{real:$('real').getValue(),identity:$('identity').getValue()},
                                 update:$('identity'),
        			 onComplete:callbackFun
        		 }).request();
        	 });
         }      

function callbackFun(response){
    var reStr=response;
    if(response.indexOf(':)')==-1){
         reStr="<font color=\"red\">"+reStr+"</font>";
    }
    return reStr;
}