Mustache

Inspired by ctemplate and et, Mustache is a framework-agnostic way to render logic-free views.

It's not a markup language because there is no language. There is no logic.

Overview

Think of Mustache as a replacement for your views. Instead of views consisting of ERB or HAML with random helpers and arbitrary logic, your views are broken into two parts: a Ruby class and an HTML template.

We call the Ruby class the "view" and the HTML template the "template."

All your logic, decisions, and code is contained in your view. All your markup is contained in your template. The template does nothing but reference methods in your view.

This strict separation makes it easier to write clean templates, easier to test your views, and more fun to work on your app's front end.

Why?

I like writing Ruby. I like writing HTML. I like writing JavaScript.

I don't like writing ERB, Haml, Liquid, Django Templates, putting Ruby in my HTML, or putting JavaScript in my HTML.

Usage

We've got an examples folder but here's the canonical one:

class Simple < Mustache
  def name
    "Chris"
  end

  def value
    10_000
  end

  def taxed_value
    value - (value * 0.4)
  end

  def in_ca
    true
  end
end

We simply create a normal Ruby class and define methods. Some methods reference others, some return values, some return only booleans.

Now let's write the template:

Hello {{name}}
You have just won ${{value}}!
{{#in_ca}}
Well, ${{taxed_value}}, after taxes.
{{/in_ca}}

This template references our view methods. To bring it all together, here's the code to render actual HTML;

Simple.new.to_html

Which returns the following:

Hello Chris
You have just won $10000!
Well, $6000.0, after taxes.

Simple.

Tag Types

Tags are indicated by the double mustaches. {{name}} is a tag. Let's talk about the different types of tags.

Variables

The most basic tag is the variable. A {{name}} tag in a basic template will try to call the name method on your view. If there is no name method, an exception will be raised.

All variables are HTML escaped by default. If you want, for some reason, to return unescaped HTML you can use the triple mustache: {{{name}}}.

Boolean Sections

A section begins with a pound and ends with a slash. That is, {{#person}} begins a "person" section while {{/person}} ends it.

If the person method exists and calling it returns false, the HTML between the pound and slash will not be displayed.

If the person method exists and calling it returns true, the HTML between the pound and slash will be rendered and displayed.

Enumerable Sections

Enumerable sections are syntactically identical to boolean sections in that they begin with a pound and end with a slash. The difference, however, is in the view: if the method called returns an enumerable, the section is repeated as the enumerable is iterated over.

Each item in the enumerable is expected to be a hash which will then become the context of the corresponding iteration. In this way we can construct loops.

For example, imagine this template:

{{#repo}}
  <b>{{name}}</b>
{{/repo}}

And this view code:

def repo
  Repository.all.map { |r| { :name => r.to_s } }
end

When rendered, our view will contain a list of all repository names in the database.

Comments

Comments begin with a bang and are ignored. The following template:

<h1>Today{{! ignore me }}.</h1>

Will render as follows:

<h1>Today.</h1>

Partials

Partials begin with a less than sign, like {{< box}}.

If a partial's view is loaded, we use that to render the HTML. If nothing is loaded we render the template directly using our current context.

In this way partials can reference variables or sections the calling view defines.

Dict-Style Views

ctemplate and friends want you to hand a dictionary to the template processor. Naturally Mustache supports a similar concept. Feel free to mix the class-based and this more procedural style at your leisure.

Given this template (dict.html):

Hello {{name}}
You have just won ${{value}}!

We can fill in the values at will:

dict = Dict.new
dict[:name] = 'George'
dict[:value] = 100
dict.to_html

Which returns:

Hello George
You have just won $100!

We can re-use the same object, too:

dict[:name] = 'Tony'
dict.to_html
Hello Tony
You have just won $100!

Templates

A word on templates. By default, a view will try to find its template on disk by searching for an HTML file in the current directory that follows the classic Ruby naming convention.

TemplatePartial => ./template_partial.html

You can set the search path using Mustache.path. It can be set on a class by class basis:

class Simple < Mustache
  self.path = File.dirname(__FILE__)
  ... etc ...
end

Now Simple will look for simple.html in the directory it resides in, no matter the cwd.

If you want to just change what template is used you can set Mustache.template_file directly:

Simple.template_file = './blah.html'

You can also go ahead and set the template directly:

Simple.template = 'Hi {{person}}!'

You can also set a different template for only a single instance:

Simple.new.template = 'Hi {{person}}!'

Whatever works.

Helpers

What about global helpers? Maybe you have a nifty gravatar function you want to use in all your views? No problem.

This is just Ruby, after all.

module ViewHelpers
  def gravatar(email, size = 30)
    gravatar_id = Digest::MD5.hexdigest(email.to_s.strip.downcase)
    gravatar_for_id(gravatar_id, size)
  end

  def gravatar_for_id(gid, size = 30)
    "#{gravatar_host}/avatar/#{gid}?s=#{size}"
  end

  def gravatar_host
    @ssl ? 'https://secure.gravatar.com' : 'http://www.gravatar.com'
  end
end

Then just include it:

class Simple < Mustache
  include ViewHelpers

  def name
    "Chris"
  end

  def value
    10_000
  end

  def taxed_value
    value - (value * 0.4)
  end

  def in_ca
    true
  end
end

Great, but what about that @ssl ivar in gravatar_host? There are many ways we can go about setting it.

Here's on example which illustrates a key feature of Mustache: you are free to use the initialize method just as you would in any normal class.

class Simple < Mustache
  include ViewHelpers

  def initialize(ssl = false)
    @ssl = ssl
  end

  ... etc ...
end

Now:

Simple.new(request.ssl?).to_html

Convoluted but you get the idea.

methodmissing/mustache