Composable HTML templating for Ruby
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README.md

Rubyoshka - Composable HTML templating for Ruby

INSTALL | TUTORIAL | EXAMPLES | REFERENCE

What is Rubyoshka

Rubyoshka is an HTML templating engine for Ruby that offers the following features:

  • HTML templating using plain Ruby syntax
  • Minimal boilerplate
  • Mix logic and tags freely
  • Use global and local contexts to pass values to reusable components
  • Automatic HTML escaping
  • Composable nested components
  • Template caching from fragments to whole templates

Note Rubyoshka is a new library and as such may be missing features and contain bugs. Also, its API may change unexpectedly. Your issue reports and code contributions are most welcome!

With Rubyoshka you can structure your templates like a Russian doll, each component containing any number of nested components, in a somewhat similar fashion to React. The name Rubyoshka is a nod to Matryoshka, the Russian nesting doll.

Installing Rubyoshka

Using bundler:

gem 'rubyoshka'

Or manually:

$ gem install rubyoshka

Getting started

To use Rubyoshka in your code just require it:

require 'rubyoshka'

Alternatively, you can import it using Modulation:

Rubyoshka = import('rubyoshka')

To create a template use Rubyoshka.new or the global method Kernel#H:

# can also use Rubyoshka.new
html = H {
  div { p 'hello' }
}

Rendering a template

To render a Rubyoshka template use the #render method:

H { span 'best span' }.render  #=> "<span>best span</span>"

The render method accepts an arbitrary context variable:

html = H {
  h1 context[:title]
}

html.render(title: 'My title') #=> "<h1>My title</h1>"

All about tags

Tags are added using unqualified method calls, and are nested using blocks:

H {
  html {
    head {
      title 'page title'
    }
    body {
      article {
        h1 'article title'
      }
    }
  }
}

Tag methods accept a string argument, a block, or no argument at all:

H { p 'hello' }.render #=> "<p>hello</p>"

H { p { span '1'; span '2' } }.render #=> "<p><span>1</span><span>2</span></p>"

H { hr() }.render #=> "<hr/>"

Tag methods also accept tag attributes, given as a hash:

H { img src: '/my.gif' }.render #=> "<img src="/my.gif"/>

H { p "foobar", class: 'important' }.render #=> "<p class=\"important\">foobar</p>"

Logic in templates

Since Rubyoshka templates are just a bunch of Ruby, you can easily write your view logic right in the template:

def user_message(user)
  H {
    if user
      span "Hello, #{user.name}!"
    else
      span "Hello, guest!"
    end
  }
end

Local context

When writing logic and referring to application values in you templates, there are some ground rules to obey. Since the template code is evaluated using #instance_eval that means that you will not be able to directly use instance variables or do unqualified method calls (calls to self).

In order to facilitate exposing values to your template logic, Rubyoshka provides an API for setting a local context. The local context is simply a set of values that are accessible for a given block of code, and to any nested blocks within it. The local context is primarily set using the #with method:

H {
  with(name: 'world') {
    div {
      span "Hello, #{name}"
    }
  }
}

The local context can alternatively be set by passing hash values to #H:

H(name: 'world') {
  div { span "Hello, #{name}" }
}

A local context can also be set for a component (see the next section) simply by passing arguments to the component call:

Greeting = H { span "Hello, #{name}" }

H {
  div {
    Greeting(name: 'world')
  }
}

Tip: accessing self and instance variables from a template

In order to be able to access the object in the context of which the template is defined or any of its methods, you can pass it in the local context:

class User
  ...
  def greeting_template
    H(user: self) {
      ...
      span "Hello, #{user.name}"
      span "your email: #{user.email}"
    }
  end
end

Instance variables can be passed to the template in a similar fashion:

H(name: @name) { span "Hello, #{name}" }

Global context

In addition to the local context, Rubyoshka also provides a way to set a global context, accessible from anywhere in the template, and also in sub-components used in the template.

The global context is a simple hash that can be accessed from within the template with the #context method:

greeting = H { span "Hello, #{context[:name]}" }

The global context can be set upon rendering the template:

greeting.render(name: 'world')

Templates as components

Rubyoshka makes it easy to compose multiple separate templates into a whole HTML document. Each template can be defined as a self-contained component that can be reused inside other components. Components should be defined as constants, either in the global namespace, or on the Rubyoshka namespace. Each component can be defined as either a Rubyoshka instance (using #H) or as a proc that returns a Rubyoshka instance:

Title = H { h1 title }

# Item is actually a Proc that returns a template
Item = ->(id:, text:, checked:) {
  H {
    li {
      input name: id, type: 'checkbox', checked: checked
      label text, for: id
    }
  }
}

def render_items(items)
  html = H {
    Title()
    ul {
      items.each { |id, attributes|
        Item id: id, text: attributes[:text], checked: attributes[:active]
      }
    }
  }.render
end

Note that a component is invoked as a method, which means that if no arguments are passed, you should add an empty pair of parens, as shown in the example above.

In addition to using components defined as constants, you can also use non-constant components by invoking the #emit method:

greeting = H { span "Hello, world" }

H {
  div {
    emit greeting
  }
}

Fragment caching

Any part of a Rubyoshka template can be cached - a fragment, a component, or a whole template. It is up to you, the user, to determine which parts of the template to cache. By default, a call to #cache creates a cache entry based on the source location of the cached block:

Head = H {
  cache {
    head {
      title 'My app'
      style "@import '/app.css';"
    }
  }
}

However, if your template references local or global variables, you'll want to take those into account when caching. This is done by passing any variables used in the template to #cache in order to create separate cache entries for each discrete value or combination of values:

Greeting = H {
  cache(name) {
    div {
      span "Hello, #{name}"
    }
  }
}

names = %w{tommy dolly world}
App = H {
  names.each { |n| Greeting(name: n) }
}

In the above example a separate cache entry will be created for each name. The use of caching in components is especially beneficial since components may be reused in multiple different templates in your app.

Changing the cache store

Rubyoshka ships with a naïve in-memory cache store built-in. You can use another cache store by overriding the Rubyoshka.cache_get and Rubyoshka.cache_set methods (see API reference).

Wrapping arbitrary HTML with a component

Components can also be used to wrap arbitrary HTML with addional markup. This is done by implementing the component as a proc that takes a block:

Header = ->(&inner_html) {
  header {
    h1 'This is a title'
    emit inner_html
  }
}

Greeting = H { span "Hello, #{name}" }

H { Header { Greeting(name: 'world') }.render #=> "<header><h1>This is a title</h1><span>Hello, world</span></header>"

Some interesting use cases

Rubyoshka opens up all kinds of new possibilities when it comes to putting together pieces of HTML. Feel free to explore the API!

Routing in the view

The following example demonstrates a router component implemented as a pure function. The router simply returns the correct component for the given path:

Router = ->(path) {
  case path
  when '/'
    PostIndex()
  when /^posts\/(.+)$/
    Post(get_post($1))
  end
}

Blog = H {
  html {
    head {
      title: 'My blog'
    }
    body {
      Topbar()
      Sidebar()
      div id: 'content' { Router(context[:path]) }
    }
  }
}

A general purpose router

A more flexible, reusable approach could be achieved by implementing a higher-order routing component, in a similar fashion to React Router:

Route = ->(path, &block) {
  match = path.is_a?(Regexp) ?
    context[:path] =~ path : context[:path] == /^#{path}/
  emit block if match
}

Blog = H {
  html {
    head {
      title: 'My blog'
    }
    body {
      Topbar()
      Sidebar()
      div id: 'content' {
        Route '/'             { PostIndex() }
        Route /^posts\/(.+)$/ { Post(get_post($1)) }
      }
    }
  }
}

A higher-order list component

Here's another demonstration of a higher-order component, a list component that takes an item component as an argument. The List component can be reused for rendering any kind of unordered list, and with any kind of item component:

List = ->(items, item_component) {
  H {
    ul {
      items.each { |item|
        with(item: item) { 
          li { emit item_component }
        }
      }
    }
  }
}

TodoItem = H {
  span item.text, class: item.completed ? 'completed' : 'pending'
}

def todo_list(items)
  H {
    div { List(items, TodoItem) }
  }
end

API Reference

Rubyoshka#initialize(**context, &block) a.k.a. Kernel#H

  • context: local context hash
  • block: template block

Initializes a new Rubyoshka instance. This method takes a block of template code, and an optional local context in the form of a hash. The Kernel#H method serves as a shortcut for creating Rubyoshka instances.

Rubyoshka#render(**context)

  • context: global context hash

Renders the template with an optional global context hash.

Methods accessible inside template blocks

#<tag/component>(*args, **props, &block)

  • args: tag arguments. For an HTML tag Rubyoshka expects a single String argument containing the inner text of the tag.
  • props: hash of tag attributes
  • block: inner HTML block

Adds a tag or component to the current template. If the method name starts with an upper-case letter, it is considered a component.

If a text argument is given for a tag, it will be escaped.

#cache(*vary, &block)

  • vary: variables used in cached block. The given values will be used to create a separate cache entry.
  • block: inner HTML block

Caches the markup in the given block, storing it in the Rubyoshka cache store. If a cache entry for the given block is found, it will be used instead of invoking the block. If one or more variables given, those will be used to create a separate cache entry.

#context

Accesses the global context.

#emit(object) a.k.a. #e(object)

  • object: Proc, Rubyoshka instance or String

Adds the given object to the current template. If a String is given, it is rendered verbatim, i.e. without escaping.

html5(&block)

  • block: inner HTML block

Adds an HTML5 doctype tag, followed by an html tag with the given block.

#text(data)

  • data - text to add

Adds text without wrapping it in a tag. The text will be escaped.

#with(**context, &block)

  • context: local context hash
  • block: HTML block

Sets a local context for use inside the given block. The previous local context will be restored upon exiting the given block.

Rubyoshka.cache

Returns the cache store. A cache store should implement two methods - #[] and #[]=. Here's an example implementing a Redis-based cache store:

class RedisTemplateCache
  def initialize(conn, prefix)
    @conn = conn
    @prefix = prefix
  end

  def [](key)
    @conn.get("#{prefix}:#{key}")
  end

  def []=(key, value)
    @conn.set("#{prefix}:#{key}", value)
  end
end

TEMPLATE_CACHE = RedisTemplaceCache.new(redis_conn, "templates:cache")

def Rubyoshka.cache
  TEMPLATE_CACHE
end