Jquery dynamically generated element (class, ID) click not working

For example

  <script type="text/javascript">

        $(document).ready(function() {

            $(".div.ajax_list").click(function() {
                $(".test").html("<button class='sendmail'>click me</button>")
            });   

            $(".sendmail").on('click',  function(){
                alert('mail is sent');
            });
        });

    </script>

You will find sendmail button did not work.
change

            $(".sendmail").on('click',  function(){
                alert('mail is sent');
            });

to

            $(".sendmail").live('click',  function(){
                alert('mail is sent');
            }); 

will fix the problem.

or

             $(document).on('click',  '.sendmail00', function(){
                alert('mail is sent');
            });

Reference:
http://stackoverflow.com/questions/6658752/click-event-doesnt-work-on-dynamically-generated-elements