Hamlbars is a Ruby gem which allows you to easily generate Handlebars templates using Haml.

For an alternative to Hamlbars, also check out Emblem, if you are using Ember.

Add the following line to your Gemfile (on Rails, inside the :assets group):

gem 'hamlbars', '~> 2.1'

As of version 2.0 Hamlbars simply outputs raw Handlebars templates, and you will need to use the precompiler of your choice to compile the assets for your usage.

If you're using Ember.js then you will need the ember-rails gem. If you're just using Handlebars templates on their own then you need to use handlebars_assets to precompile for your framework.

Be sure to take a look at Hamlbars' sister project FlavourSaver for pure-ruby server-side rendering of Handlebars templates.

As of version 2.1 Hamlbars emits bind-attr instead of bindAttr for bound element attributes. If you are running an older version of Ember, then keep your Gemfile pinned to ~> 2.0 until you upgrade.

When using the handlebars_assets or ember-rails gems you need to add an extra file extension so that the asset pipeline knows to take the output of Hamlbars and send it into the template compiler of your choice. Luckily both gems register the hbs extension, so you can enable asset compilation by setting .js.hbs.hamlbars as the file extension for your templates.

If you're unsure how all the pieces fit together then take a quick look at the demo site.

Hamlbars adds a couple of extensions to Haml in order to allow you to create handlebars expressions in your templates.

You can use the handlebars helper (or just hb for short) to generate both Handlebars blocks and expressions.

Generating Handlebars expressions is as simple as using the handlebars helper and providing the expression as a string argument:

= hb 'App.widgetController.title'

which will will generate:

{{App.widgetController.title}}

Whereas passing a block to the handlebars helper will create a Handlebars block expression:

%ul.authors
= hb 'each authors' do
  %li<
    = succeed ',' do
      = hb 'lastName'
    = hb 'firstName'

will result in the following markup:

<ul class="authors">
   {{#each authors}}
     <li>{{lastName}}, {{firstName}}</li>
   {{/each}}
</ul>

If/else statements follow the same pattern as blocks, but with the caveat that the else statement must be nested within the original if block. If you'd like more information, check out the comments in #15.

= hb 'if isSignedIn' do
  Welcome,
  = hb 'firstName'

  = hb 'else' / Notice this line is indented within the original if statement.
  Hello! / Notice this line is indented inline with the else statement.

Compiles to:

{{#if isSignedIn}}
  Welcome,
  {{firstName}}
{{else}}
  Hello!
{{/if}}

The hb helper can take an optional hash of options which will be rendered inside the expression:

= hb 'view App.InfoView', :tagName => 'span'

will result in:

{{view App.InfoView tagName="span"}}

You can use the handlebars! or hb! variant of the handlebars helper to output "tripple-stash" expressions within which Handlebars does not escape the output.

Unfortunately, (or fortunately) due to the nature of Haml, we can't put Handlebars expressions in a tag definition, eg:

<{{tagName}}>
  My content
</{{tagName}}>

But we can allow you to put Handlebars expressions in to generate tag arguments by adding a special hb attribute to your tags. For example:

%div{:hb => 'idHelper'}

Which would render the following:

<div {{idHelper}}></div>

If you need to place more than one expression inside your tag then you can pass an array of expressions.

A large portion of the audience for Hamlbars is using it to generate templates for sites using the Ember.js javascript framework. We have added some special extra syntax to cater for Ember's common idioms.

You can easily add attribute bindings by adding a :bind hash to the tag attributes, like so:

%div{ :class => 'widget', :bind => { :title => 'App.widgetController.title' }

Which will generate the following output:

<div class="widget" {{bindAttr title="App.widgetController.title"}}></div>

To use Ember's {{action}} helper, set the :_action attribute, like so:

%a{ :_action => 'toggle' } Toggle
%a{ :_action => 'edit article on="doubleClick"' } Edit

This will generate:

<a {{action "toggle"}}>Toggle</a>
<a {{action "edit" article on="doubleClick"}}>Edit</a>

Note that :_action has a leading underscore, to distinguish it from regular HTML attributes (<form action="...">).

You can enable support by calling Hamlbars::Template.enable_rails_helpers!. Probably the best way to do this is to create an initializer. This is dangerous and possibly stupid as a large number of Rails' helpers require access to the request object, which is not present when compiling assets.

That said, it can be pretty handy to have access to the route helpers.

Use at your own risk. You have been warned.

Hamlbars is Copyright © 2012 Sociable Limited and licensed under the terms of the MIT License.