Dancer2::Plugin::Deferred - Defer messages or data across redirections


version 0.007018


  use Dancer2::Plugin::Deferred;

  get '/defer' => sub {
    deferred error => "Klaatu barada nikto";
    redirect '/later';

  get '/later' => sub {
    template 'later';

  # in template ''
  <% IF deferred.error %>
  <div class="error"><% deferred.error %></div>
  <% END %>


This Dancer2 plugin provides a method for deferring a one-time message across a redirect. It is similar to "flash" messages, but without the race conditions that can result from multiple tabs in a browser or from AJAX requests. It is similar in design to Catalyst::Plugin::StatusMessage, but adapted for Dancer2.

It works by creating a unique message ID within the session that holds deferred data. The message ID is automatically added as a query parameter to redirection requests. It's sort of like a session within a session, but tied to a request rather than global to the browser. (It will even chain across multiple redirects.)

When a template is rendered, a pre-template hook retrieves the data and deletes it from the session. Alternatively, the data can be retrieved manually (which will also automatically delete the data.)

Alternatively, the message ID parameters can be retrieved and used to construct a hyperlink for a message to be retrieved later. In this case, the message is preserved past the template hook. (The template should be sure not to render the message if not desired.)



  deferred $key => $value;
  $value = deferred $key; # also deletes $key

This function works just like var or session, except that it lasts only for the current request and across any redirects. Data is deleted if accessed. If a key is set to an undefined value, the key is deleted from the deferred data hash.


  template 'index', { deferred => all_deferred };

This function returns all the deferred data as a hash reference and deletes the stored data. This is called automatically in the before_template_render hook, but is available if someone wants to have manual control.


  template 'index' => { link => uri_for( '/other', { deferred_param } ) };

This function returns the parameter key and value used to propagate the message to another request. Using this function toggles the var_keep_key variable to true to ensure the message remains to be retrieved by the link.




Thank you to mst for explaining why Catalyst::Plugin::StatusMessages does what it does and putting up with my dumb ideas along the way.


  • David Golden <>

  • Yanick Champoux <>

  • Deluxaran <>


This software is Copyright (c) 2018, 2016 by David Golden.

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004