Snazzy Mustaches: Handlebars templating

I had been playing around with Mustache, and Yanick's fantastic plugin for Dancer2, Dancer2::Plugin::Mustache, when I bumped into its steroid-fed brother system, Handlebars, and its beautiful system for implementing additional custom helpers into the templates. Yanick had written a Mustache plugin for earlier Dancer, but there wasn't one for Dancer2. So I shamelessly plagarized, remixed those two modules, and released my very first module to CPAN.

About Handlebars

Handlebars, like Mustache, is a minimalist templating system. Like Template Toolkit, it provides for variable substitution, including nested objects. Unlike Template Toolkit, though, neither Handlebars nor Mustache ships with a large suite of useful functions; creating those is left up to you, with both showing in their documentation that those can be easily created in JavaScript within the calling page.

Where they differ, most critically to me, is that Handlebars includes a few logical helpers, where Mustache does not. Those are nice to have--#if, #unless, #with, and #each are so ubiquitously used, that it's very useful to have those shipped with the system. As Yanick worked out in his Dancer plugin for it, it's relatively straightforward to write any helpers you need in Perl.

So how do I use it in my application?

Simply specify it as your template system in your config.yml:

template: handlebars
       - MyApp::HandlebarsHelpers

...and name your templates using the suffix .hbs. Then, in your route code:

get '/style/:style' => sub {
   template 'style' => {
      style => route_parameters->get('style'),

Your template, named style.hbs, might look something like this:

Why, that's a lovely {{style}} mustache you have!

It works a lot like Template Toolkit, as you can see here.


Loops are equally easy in Handlebars. Suppose you had sent to your template an arrayref people, each of which had fields name and hometown. You could print that out as a bulleted list like so, in your template:

{{#each people}}
  <li>{{}} is from {{this.hometown}}.</li>

In the built-in helpers, this will represent the current context or object, and it's always available to you inside these loops. No more of this:

[% FOREACH person IN people %]

...just use this!

Custom Helpers

You can write a custom helper to take any data you like, and wrap some structure around it in the output HTML, and with this setup, you just specify where that module of helpers lives in your config.yml, as I did above. Then, write your code, like so:

package MyApp::HandlebarsHelpers;
use parent Dancer2::Template::Handlebars::Helpers;

sub shout :Helper {
   my( $context, $text ) = @_;
   return '<b>' . uc $text . '</b>';


You always get the full context at the time of the call, so any page variable (including this, if you're inside a loop) can be used. You can specify additional parameters in the call, too, so this template call:

{{ shout('Hey') }}, friend. Don't forget to wax your mustache!

would output:

HEY, friend. Don't forget to wax your mustache!

Happy Dancing, from the Plugins Princess.

I joined the Dancer core team this year, and it seems to be the case that I am emerging as the Princess of the Plugins. It's not like I've released a whole bunch of them--there are only four on CPAN. But there are more coming down the road!

Whatever holidays you and the people you love celebrate at this time of year, I hope they are happy and fulfilling. Happy Dancing, and see you in 2024!


This article was written by D Ruth Holloway for the Dancer Advent Calendar 2023.