FlavourSaver

Handlebars.js without the .js

WAT?

FlavourSaver is a ruby-based implementation of the Handlebars.js templating language. FlavourSaver supports Handlebars template rendering natively on Rails and on other frameworks (such as Sinatra) via Tilt.

Please use it, break it, and send issues/PR's for improvement.

Caveat

FlavourSaver is used in production by a lot of folks, none of whom are me. As I don't use FlavourSaver in my daily life I will not be responding to issues unless they have a corresponding PR. If you'd like to take over maintaining this project then get in contact.

License

Installation

Add this line to your application's Gemfile:

gem 'flavour_saver'

And then execute:

$ bundle

Or install it yourself as:

$ gem install flavour_saver

Usage

FlavourSaver provides an interface to the amazing Tilt templating library, meaning that it should work with anything that has Tilt support (Sinatra, etc) and has a native Rails template handler.

Status

FlavourSaver is in its infancy, your pull requests are greatly appreciated.

Currently supported:

Full support of Mustache and Handlebars templates.
Expressions:
- with object-paths ({{some.method.chain}})
- containing object-literals ({{object.['index'].method}}): Ruby's :[](index) method is called for literals, making FlavourSaver compatible with Hash and hashlike objects.
- with list arguments ({{method arg1 "arg2"}})
- with hash arguments ({{method foo=bar bar="baz"}})
- with list and hash arguments ({{method arg1 arg2 foo=bar bar="baz"}}) provided that the hash is the last argument.
- Comments ({{! a comment}})
- Expression output is HTML escaped
Safe expressions
- Expressions wrapped in triple-stashes are not HTML escaped ({{{an expression}}})
Block expressions
- Simple API for adding block helpers.
- Block expressions with inverse blocks
- Inverse blocks
Partials
Raw content ({{{{raw}}}} not parsed or validated {{{{/raw}}}})
Subexpressions ({{sum 1 (sum 1 1)}} returns 3)

Helpers

FlavourSaver implements the following helpers by default:

#with

Yields its argument into the context of the block contents:

{{#with person}}
  {{name}}
{{/with}}

#each

Takes a single collection argument and yields the block's contents once for each member of the collection:

{{#each people}}
  {{name}}
{{/each}}

#if

Takes a single argument and yields the contents of the block if that argument is truthy.

{{#if person}}
  Hi {{person.name}}!
{{/if}}

It can also handle a special case {{else}} expression:

{{#if person}}
  Hi {{person.name}}!
{{else}}
  Nobody to say hi to.
{{/if}}

#unless

Exactly the same is #if but backwards.

this

In JavaScript this is a native keyword, in Ruby not-so-much. FlavourSaver's this helper returns self:

{{#each names}}
  {{this}}
{{/each}}

log

Writes log output. The destination can be changed by assigning a Logger instance to FlavourSaver.logger=. On Rails FlavourSaver.logger automatically points at Rails.logger.

Adding additional helpers

Additional helpers can easy be added by calling FS.register_helper, eg:

FS.register_helper(:whom) { 'world' }

Now if you were to render the following template:

<h1>Hello {{whom}}!</h1>

You would receive the following output:

<h1>Hello world!</h1>

Adding block helpers

Creating a block helper works exactly like adding a regular helper, except that the helper implementation can call yield.contents one or more times, with an optional argument setting the context of the block execution:

FS.register_helper(:three_times) do
  yield.contents
  yield.contents
  yield.contents
end

Which when called with the following template:

{{#three_times}}
  hello
{{/three_times}}

would result in the following output:

  hello
  hello
  hello

Implementing a simple iterator is dead easy:

FS.register_helper(:list_people) do |people|
  people.each do |person|
    yield.contents person
  end
end

Which could be used like so:

{{#list_people people}}
  <b>{{name}}<b><br />
  Age: {{age}}<br />
  Sex: {{sex}}<br />
{{/list_people}}

Block helpers can also contain an {{else}} statement, which, when used creates a second set of block contents (called inverse) which can be yielded to the output:

FS.register_helper(:isFemale) do |person,&block|
  if person.sex == 'female'
    block.call.contents
  else
    block.call.inverse
  end
end

You can also register an existing method:

def isFemale(person)
  if person.sex == 'female'
    yield.contents
  else
    yield.inverse
  end
end

FS.register_helper(method(:isFemale))

Which could be used like so:

{{#isFemale person}}
  {{person.name}} is female.
{{else}}
  {{person.name}} is male.
{{/isFemale}}

Subexpressions

You can use a subexpression as any value for a helper, and it will be executed before it is ran. You can also nest them, and use them in assignment of variables.

Below are some examples, utilizing a "sum" helper than adds together two numbers.

{{sum (sum 5 10) (sum 2 (sum 1 4))}}
#=> 22

{{#if (sum 1 2) > 2}}its more{{/if}}
#=> its more

{{#student_heights size=(sum boys girls)}}

Raw Content

Sometimes you don't want a section of content to be evaluted as handlebars, such as when you want to display it in a page that renders with handlebars. FlavourSaver offers a raw helper, that will allow you to pass anything through wrapped in those elements, and it will not be evaluated.

{{{{raw}}}}
{{if} this tries to parse, it will break on syntax
{{{{/raw}}}}
=> {{if} this tries to parse, it will break on syntax

Its important to note that while this looks like a block helper, it is not in practice. This is why you must omit the use of a # when writing it.

Using Partials

Handlebars allows you to register a partial either as a function or a string template with the engine before compiling, FlavourSaver retains this behaviour (with the notable exception of within Rails - see below).

To register a partial you call FlavourSaver.register_partial with a name and a string:

FlavourSaver.register_partial(:my_partial, "{{this}} is a partial")

You can then use this partial within your templates:

{{#each people}}{{> my_partial this}}{{/each}}

Using with Rails

One potential gotcha of using FlavourSaver with Rails is that FlavourSaver doesn't let you have any access to the controller's instance variables. This is done to maintain compatibility with the original JavaScript implementation of Handlebars so that templates can be used on both the server and client side without any change.

When accessing controller instance variables you should access them by way of a helper method or a presenter object.

For example, in ApplicationController.rb you may have a before_filter which authenticates the current user's session cookie and stores it in the controller's @current_user instance variable.

To access this variable you could create a simple helper method in ApplicationHelpers:

def current_user
  @current_user
end

Which would mean that you are able to access it in your template:

{{#if current_user}}
  Welcome back, {{current_user.first_name}}!
{{/if}}

Using the Tilt Interface Directly

You can use the registered Tilt interface directly to render template strings with a hash of template variables.

The Tilt template's render method expects an object that can respond to messages using dot notation. In the following example, the template variable {{foo}} will result in a call to .foo on the data object. For this reason the data object can't be a simple hash. A model would work, but if you have a plain old Ruby hash, use it to create a new OpenStruct object, which will provide the dot notation needed.

template = Tilt['handlebars'].new { "{{foo}} {{bar}}" }
data = OpenStruct.new foo: "hello", bar: "world"

template.render data # => "hello world"

Special behaviour of Handlebars' partial syntax

In Handlebars.js all partial templates must be pre-registered with the engine before they are able to be used. When running inside Rails FlavourSaver modifies this behaviour to use Rails' render partial helper:

{{> my_partial}}

Will be translated into:

render :partial => 'my_partial'

Handlebars allows you to send a context object into the partial, which sets the execution context of the partial. In Rails this behaviour would be confusing and non-standard, so instead any argument passed to the partial is evaluated and passed to the partial's :object argument:

{{> my_partial my_context}}

render :partial => 'my_partial', :object => my_context

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Added some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request