http://stackoverflow.com/questions/366311/how-do-you-handle-rails-flash-with-ajax-requests
参考上面的文章就行了。。我只看懂了下面的一种，能够实现。。。。：
controller
respond_to do |format|
flash.now[:notice] = @msg / 'blah blah...'
format.html
format.js
end
view
<div id='notice'>
<%= render :partial => 'layouts/flash' , :locals => { :flash => flash } %>
</div>
layouts/_flash.html.erb
<% flash.each do |name, msg| %>
<div class="alert-message info">
<a class="close dismiss" href="#">x</a>
<p><%= msg %></p>
</div>
<% end %>
post.js.erb
$("#notice").html("<%= escape_javascript(render :partial => 'layouts/flash' , :locals => { :flash => flash }).html_safe %>");
