application.js

$(function() {
  $('#add_new').click(function() {
    TopUp.display($('#topup_div'), 
                  {type: 'dom', title: 'New Todo', 
                   overlayClose: 1, resizable: 0, shaded: 1});      
  }); 
  $('#topup_frm').submit(function() {
    $.post(this.action, $(this).serialize(), null, "script");
    return false;
  });

  // Setup the ajax indicator
  $("body").append('<div id="ajaxBusy"><p><img src="/images/loading.gif"></p></div>');
  $('#ajaxBusy').css({
    display:"none",
    margin:"0px",
    paddingLeft:"0px",
    paddingRight:"0px",
    paddingTop:"0px",
    paddingBottom:"0px",
    position:"fixed",
    right:"1px",
    top:"1px",
    width:"auto"
  });

  // Ajax activity indicator bound 
  // to ajax start/stop document events
  $(document).ajaxStart(function(){ 
    $('#ajaxBusy').show(); 
  }).ajaxStop(function(){ 
    $('#ajaxBusy').hide();
  });

  $.ajaxSetup({
    error:function(x,e){
      if(x.status==0){
        alert('You are offline!!\n Please Check Your Network.');
      }else if(x.status==404){
        $.achtung( {message: 'Error: Requested URL not found.', className: 'achtungFail', timeout: 0} );
      }else if(x.status==500){
        $.achtung( {message: 'Error: Internel Server Error.', className: 'achtungFail', timeout: 0} );
      }else if(e=='parsererror'){
        $.achtung( {message: 'Error: Parsing JSON Request failed.', className: 'achtungFail', timeout: 0} );
      }else if(e=='timeout'){
        $.achtung( {message: 'Error: Request Time Out.', className: 'achtungFail', timeout: 0} );
      }else {
        $.achtung( {message: 'Error: ' + x.responseText, className: 'achtungFail', timeout: 0} );
      }
    }
  });
});

create.js.erb

var elem = "<tr><td><%= @todo.txt -%></td></tr>";
$(elem).insertBefore("#todo_tbl tr:first-child")

new.html.erb

<a href='#' id='add_new'>Add new</a>
<table id='todo_tbl'>
  <tr>
    <td>Todo 1</td>
  </tr>
  <tr>
    <td>Todo 2</td>
  </tr>
  <tr>
    <td>Todo 3</td>
  </tr>
</table>

<div id='topup_div'>
  <% form_for Todo.new, :html => {:id= > 'topup_frm'} do |f| %>
    <%= f.text_field 'text' %>
    <%= f.submit 'Save' %>
  <% end %>
</div>

tasks_controller.rb

def create
  @todo = Todo.new(params[:todo])
  
  if @todo.save
    respond_to do |fmt|
      fmt.js
    end
  else
    respond_to do |fmt|
      fmt.js { render :js => 'alert("Error saving todo.");'}
    end
  end
end