How do you handle Rail's flash with Ajax requests?

You can also store the flash messages in the response headers using a after_filter block and display them using javascript:

class ApplicationController < ActionController::Baseafter_filter :flash_to_headersdef flash_to_headers  return unless request.xhr?  response.headers['X-Message'] = flash[:error]  unless flash[:error].blank?  # repeat for other flash types...  flash.discard  # don't want the flash to appear when you reload pageend

And in application.js add a global ajax handler. For jquery do something like this:

$(document).ajaxError(function(event, request) {  var msg = request.getResponseHeader('X-Message');  if (msg) alert(msg);});

Replace alert() with your own javascript flash function or try jGrowl.

And here is my version based on @emzero, with modifications to work with jQuery, tested on Rails 3.2

application_controller.rb

class ApplicationController < ActionController::Base    protect_from_forgery    after_filter :flash_to_headers    def flash_to_headers        return unless request.xhr?        response.headers['X-Message'] = flash_message        response.headers["X-Message-Type"] = flash_type.to_s        flash.discard # don't want the flash to appear when you reload page    end    private    def flash_message        [:error, :warning, :notice].each do |type|            return flash[type] unless flash[type].blank?        end    end    def flash_type        [:error, :warning, :notice].each do |type|            return type unless flash[type].blank?        end    endend

application.js

// FLASH NOTICE ANIMATIONvar fade_flash = function() {    $("#flash_notice").delay(5000).fadeOut("slow");    $("#flash_alert").delay(5000).fadeOut("slow");    $("#flash_error").delay(5000).fadeOut("slow");};fade_flash();var show_ajax_message = function(msg, type) {    $("#flash-message").html('<div id="flash_'+type+'">'+msg+'</div>');    fade_flash();};$(document).ajaxComplete(function(event, request) {    var msg = request.getResponseHeader('X-Message');    var type = request.getResponseHeader('X-Message-Type');    show_ajax_message(msg, type); //use whatever popup, notification or whatever plugin you want});

layout: application.html.haml

        #flash-message            - flash.each do |name, msg|                = content_tag :div, msg, :id => "flash_#{name}"

This is needed in the js response

If you are using RSJ:

page.replace_html :notice, flash[:notice]flash.discard

If you are using jQuery:

$("#flash_notice").html(<%=escape_javascript(flash.delete(:notice)) %>');