Inject AJAX MooTools response

I have a form where the user will input a text and when he submits the form, the text I want must be injected, I think, or simply attached to the page like AJAX comments, but my problem is that I can get the message on the page.

I have the code working tested (I have alert the message and other stuff).

Here's my code:

en4.questionanswer = {

 postAnswer : function() {
   var mess = $('a_mess');
   var user_id = $('q_user_id');
   var question_id = $('question_id');
   //check if value is blank

   //post Question
   var request = new Request.JSON({
     'method' : 'post',
     'url' :  en4.core.baseUrl + 'question/postans',
     'data' : {
       'mess' : mess.value,            
       'question_开发者_StackOverflow中文版id' : question_id.value                                   
     },
     'onComplete':function(responseObject) {
        if( typeof(responseObject)!="object") {
          //alert('ERR');
        }
        else {                                
          if (responseObject.result == "success") {                        
            mess.value=''; //clear text after submiting
            // en4.questionanswer.start("1");
            alert(responseObject.answer);
          }
          else {                        
            alert(responseObject.message);
          }            
        }
      }
    });
    request.send();
  }
});

In the PHP part I have:

echo json_encode(array("result" => "success",
                       "message" => "Post message successful!",
                       "answer" => $content));

If responseObject.answer is the answer you are trying to place in the page this will get you started.

replace the alert(responseObject.answer) in the onComplete function with:

new Element('div': {
    html: responseObject.answer,
    class: 'optionalClassName'
}).inject($(document.body));

Replace $(document.body) with any selector you would like example:

$('comments')

or

$$('#comments .someOther > .selector')

The information provided in your post was very limited so if I missed the mark I apologize, just trying to point you in the right direction.