A simple, yet powerful templating engine for Ruby on Rails, inspired by Laravel Blade.
RBlade is a simple, yet powerful templating engine for Ruby on Rails, inspired by Laravel Blade. Unlike other Rails templating engines, RBlade prioritises the use of components and partials within templates.
RBlade template files use the .rblade file extension and are typically stored in the app/views directory.
Add RBlade to your Rails project by adding it to your Gemfile:
bundle add rblade
RBlade will automatically be detected and start parsing templates ending in .rblade.
For a quick overview of RBlade’s capabilities, refer to the reference file or take a look at the examples.
You can display data that is passed to your RBlade views by wrapping the variable in curly braces. For example, given the following controller method:
def index
@name = "Samantha"
end
You can display the contents of the name variable like so:
Hello, {{ @name }}.
[!NOTE]
RBlade’s{{ }}print directives are automatically sent through Rails’hfunction to prevent XSS attacks.
You are not limited to displaying the contents of the variables passed to the view. You can also print the results of any Ruby function. In fact, you can put any Ruby code you wish inside of a RBlade print directive:
The current UNIX timestamp is {{ Time.now.to_i }}.
By default, RBlade {{ }} directives are automatically sent through Rails’ h function to prevent XSS attacks. If you do not want your data to be escaped, you can use the following syntax:
Hello, {!! @name !!}.
[!WARNING]
Be very careful when printing content that is supplied by users of your application. You should typically use the escaped, double curly brace syntax to prevent XSS attacks when displaying user supplied data.
For the most part, RBlade templates are backwards compatible with the built in ERB templates. Anything that works in an ERB template should also work in an RBlade template.
This includes helper methods, path helpers and methods from third party gems such as simple_forms or vite-ruby. It additionally includes the ERB syntax for outputting data, <%= ... %>, and running ruby code, <%= ... %>.
Since many JavaScript frameworks also use “curly” braces to indicate a given expression should be displayed in the browser, you can use the @ symbol to inform the RBlade rendering engine an expression should remain untouched. For example:
<h1>Laravel</h1>
Hello, @{{ name }}.
In this example, the @ symbol will be removed by RBlade; however, {{ name }} expression will remain untouched by the RBlade engine, allowing it to be rendered by your JavaScript framework.
The @ symbol can also be used to escape RBlade directives:
{{-- RBlade template --}}
@@if()
<!-- HTML output -->
@if()
@verbatim DirectiveIf you are displaying JavaScript variables in a large portion of your template, you can wrap the HTML in the @verbatim directive so that you do not have to prefix each RBlade print directive with an @ symbol:
@verbatim
<div class="container">
Hello, {{ name }}.
</div>
@endverbatim
In addition to template inheritance and displaying data, RBlade also provides convenient shortcuts for common Ruby control structures, such as conditional statements and loops. These shortcuts provide a very clean, terse way of working with Ruby control structures while also remaining familiar to their ruby counterparts.
[!NOTE]
RBlade directives are case insensitive and ignore underscores, so depending on your preference, all of@endIf,@endIfand@end_ifare identical.
You can construct if statements using the @if, @elseIf, @else, @endIf, @unless, and @endUnless directives. These directives function identically to their Ruby counterparts:
@unless(records.nil?)
@if (records.count === 1)
I have one record!
@elseIf (records.count > 1)
I have multiple records!
@else
I don't have any records!
@endIf
@endUnless
In addition to the conditional directives above, the @blank?, defined?, @empty?, @nil? and @present directives can be used as convenient shortcuts:
@present?(records)
// records is defined and is not nil
@else
// Since these directives are compiled to if statements, you can also use the @else directive
@endempty?
You can check if the application is running in the production environment using the @production directive:
@production
// Production specific content...
@endProduction
Or, you can determine if the application is running in a specific environment using the @env directive:
@env('staging')
// The application is running in "staging"...
@endEnv
@env(['staging', 'production'])
// The application is running in "staging" or "production"...
@endEnv
Case statements can be constructed using the @case, @when, @else and @endCase directives:
@case(i)
@when(1)
First case...
@when(2)
Second case...
@else
Default case...
@endCase
In addition to conditional statements, RBlade provides simple directives for working with Ruby’s loop structures:
@for (i in 0...10)
The current value is {{ i }}
@endFor
{{-- Compiles to users.each do |user| ... --}}
@each (user in users)
<p>This is user {{ user.id }}</p>
@endEach
{{-- Compiles to users.each_with_index do |user, index| ... --}}
@eachWithIndex (user, index in users)
<p>This is user {{ index }} {{ user.name }}</p>
@endEachWithIndex
{{-- eachWithIndex has a special case for Hashes: in this example, the result is "Item 1: a A" --}}
@eachWithIndex (key, value, index in {a: 'A'})
Item #{{ index + 1 }}: {{ key }} {{ value }}
@endEachWithIndex
@forElse (name in [])
<li>{{ name }}</li>
@empty
<p>No names</p>
@endForElse
@eachElse (user in users)
<li>{{ user.name }}</li>
@empty
<p>No users</p>
@endEachElse
@eachWithIndexElse (user, index in users)
<li>{{ index }}: {{ user.name }}</li>
@empty
<p>No users</p>
@endEachWithIndexElse
@while (true)
<p>I'm looping forever.</p>
@endWhile
When using loops you can also skip the current iteration or end the loop using the @next and @break directives:
for (user in users)
@if (user.type == 1)
@next
@endIf
<li>{{ user.name }}</li>
@if (user.number == 5)
@break
@endIf
@endFor
You can also include the continuation or break condition within the directive declaration:
@for (user in users)
@next(user.type == 1)
<li>{{ user.name }}</li>
@break(user.number == 5)
@endFor
The @class directive conditionally adds CSS classes. The directive accepts a Hash of classes where the key contains the class or classes you wish to add, and the value is a boolean expression:
@ruby
isActive = false;
hasError = true;
@endRuby
<span @class({
"p-4": true,
"font-bold": isActive,
"text-gray-500": !isActive,
"bg-red": hasError,
})></span>
<span class="p-4 text-gray-500 bg-red"></span>
Likewise, the @style directive can be used to conditionally add inline CSS styles to an HTML element:
@ruby
isActive = true;
@endRuby
<span @style({
"background-color: red": true,
"font-weight: bold" => isActive,
})></span>
<span style="background-color: red; font-weight: bold;"></span>
For convenience, you can use the @checked directive to easily indicate if a given HTML checkbox input is “checked”. This directive will print checked if the provided condition evaluates to true:
<input type="checkbox"
name="active"
value="active"
@checked(user.active)) />
Likewise, the @selected directive can be used to indicate if a given select option should be “selected”:
<select name="version">
@each (version in product.versions)
<option value="{{ version }}" @selected(version == selectedVersion)>
{{ version }}
</option>
@endEach
</select>
Additionally, the @disabled directive can be used to indicate if a given element should be “disabled”:
<button type="submit" @disabled(isDisabled)>Submit</button>
Moreover, the @readonly directive can be used to indicate if a given element should be “readonly”:
<input type="email"
name="email"
value="[email protected]"
@readonly(!user.isAdmin) />
In addition, the @required directive can be used to indicate if a given element should be “required”:
<input type="text"
name="title"
value="title"
@required(user.isAdmin) />
@once DirectiveThe @once directive allows you to define a portion of the template that will only be evaluated once per rendering cycle. This can be useful for pushing a given piece of JavaScript into the page’s header using stacks. For example, if you are rendering a given component within a loop, you may wish to only push the JavaScript to the header the first time the component is rendered:
@once
@push('scripts')
<script>
// Your custom JavaScript...
</script>
@endPush
@endOnce
Since the @once directive is often used in conjunction with the @push or @prepend directives, the @pushOnce and @prependOnce directives are available for your convenience:
@pushOnce('scripts')
<script>
{{-- Your javascript --}}
</script>
@endPushOnce
Additionally, you can pass an argument to the @once directive, or a second argument to the @pushonce and @prependonce directives to set the key that is used to determine if that block has already been output:
@once(:heading)
<h1>Home page</h1>
@endOnce
{{-- This block will not be output --}}
@once(:heading)
<h1>Some other title</h1>
@endOnce
[!NOTE]
The keys you use for@once,@pushOnceand@prependOnceare shared.
In some situations, it’s useful to embed Ruby code into your views. You can use the RBlade @ruby directive to execute a block of plain Ruby within your template:
@ruby
counter = 1;
@endRuby
RBlade also allows you to define your own directives using the RBlade.register_directive_handler
method. When the compiler encounters the custom directive, it will call the provided block and
output the returned value.
RBlade::register_directive_handler('sum') do |args|
args.inject(0) { |sum, num| sum + num.to_i }
end
@sum(1) -> 1
@sum(1, 2) -> 3
@sum(1, 2, 3) -> 6
RBlade also allows you to define comments in your views. However, unlike HTML comments, RBlade comments are not included in the HTML returned by your application. These comments are removed from the cached views so they have no performance downsides.
{{-- This comment will not be present in the rendered HTML --}}
Components are a way of including sub-views into your templates. To illustrate how to use them, we will create a simple alert component.
First, we will create a new alert.rblade file in the app/views/components/forms directory. Templates in the app/views/components directory and its subdirectories are are automatically discovered as components, so no further registration is required. Both .rblade and .html.rblade are valid extensions for RBlade components.
Once your component has been created, it can be rendered using its tag alias:
<x-forms.alert/>
To display a component, you can use a RBlade component tag within one of your RBlade templates. RBlade component tags start with the string x- followed by the kebab case name of the component class:
{{-- Render the `alert` component in app/views/components/ --}}
<x-alert/>
{{-- Render the `user-profile` component in app/views/components/ --}}
<x-user-profile/>
If the component class is in a subdirectory of app/views/components, you can use the . character to indicate directory nesting. For example, for the component app/views/components/form/inputs/text.rblade, we render it like so:
{{-- Render the `text` component in app/views/components/form/inputs/ --}}
<x-form.inputs.text/>
When writing components for your own application, components are automatically discovered within the app/views/components directory. Additionally, layouts in the app/views/layouts directory are automatically discovered with the layout namespace, and all views in the app/views directory are discovered with the view namespace.
Namespaced components can be rendered using the namespace as a prefix to the name separated by “::”:
{{-- Render the `app` component in app/views/layouts/ --}}
<x-layout::app/>
{{-- Render the `home` component in app/views/ --}}
<x-view::home/>
You can pass data to RBlade components using HTML attributes. Hard-coded strings can be passed to the component using simple HTML attribute strings. Ruby expressions and variables should be passed to the component via attributes that use the : character as a prefix:
<x-alert type="error" :message="message"/>
You can define a component’s data properties using a @props directive at the top of the component. You can then reference these properties using local variables within the template:
{{-- alert.rblade --}}
@props(type: "warning", message: required)
<div class="{{ type }}">{{ message }}</div>
The @props directive accepts a Hash where the key is the name of the attribute, and the value is the default value for the property. You can use the special required value to represent a property with no default that must always be defined:
{{-- This will give an error because the alert component requires a message propery --}}
<x-alert/>
All properties in the @props directive are automatically removed from attributes. Properties with names that aren’t valid Ruby variable names or are Ruby reserved keywords are not created as local variables. However, you can reference them via the attributes local variable:
@props("for": required, "data-value": nil)
<div>{{ attributes[:for] }} {{ attributes[:'data-value'] }}</div>
When passing attributes to components, you can also use a “short attribute” syntax. This is often convenient since attribute names frequently match the variable names they correspond to:
{{-- Short attribute syntax... --}}
<x-profile :user_id :name />
{{-- Is equivalent to... --}}
<x-profile :user-id="user_id" :name="name" />
Since some JavaScript frameworks such as Alpine.js also use colon-prefixed attributes, you can use a double colon (::) prefix to inform RBlade that the attribute is not a Ruby expression. For example, given the following component:
<x-button ::class="{ danger: isDeleting }">
Submit
</x-button>
The following HTML will be rendered by RBlade:
<button :class="{ danger: isDeleting }">
Submit
</button>
We’ve already examined how to pass data attributes to a component; however, sometimes you can need to specify additional HTML attributes, such as class, that are not part of the data required for a component to function. Typically, you want to pass these additional attributes down to the root element of the component template. For example, imagine we want to render an alert component like so:
<x-alert type="error" :message class="mt-4"/>
All of the attributes that are not part of the component’s constructor will automatically be added to the component’s “attribute manager”. This attribute manager is automatically made available to the component via the attributes variable. All of the attributes can be rendered within the component by printing this variable:
<div {{ attributes }}>
<!-- Component content -->
</div>
Sometimes you can need to specify default values for attributes or merge additional values into some of the component’s attributes. To accomplish this, you can use the attribute manager’s merge method. This method is particularly useful for defining a set of default CSS classes that should always be applied to a component:
<div {{ attributes.merge({"class": "alert alert-#{type}"}) }}>
{{ message }}
</div>
If we assume this component is utilized like so:
<x-alert type="error" :message class="mb-4"/>
The final, rendered HTML of the component will appear like the following:
<div class="alert alert-error mb-4">
<!-- Contents of the message variable -->
</div>
Both the class and style attributes are combined this way when using the attributes.merge method.
When merging attributes that are not class or style, the values provided to the merge method will be considered the “default” values of the attribute. However, unlike the class and style attributes, these defaults will be overwritten if the attribute is defined in the component tag. For example:
<button {{ attributes.merge({type: "button"}) }}>
{{ slot }}
</button>
To render the button component with a custom type, it can be specified when consuming the component. If no type is specified, the button type will be used:
<x-button type="submit">
Submit
</x-button>
The rendered HTML of the button component in this example would be:
<button type="submit">
Submit
</button>
Sometimes you may wish to merge classes if a given condition is true. You can accomplish this via the class method, which accepts a Hash of classes where the array key contains the class or classes you wish to add, while the value is a boolean expression:
<div {{ attributes.class({'p-4': true, 'bg-red': hasError}) }}>
{{ message }}
</div>
If you need to merge other attributes onto your component, you can chain the merge method onto the class method:
<button {{ attributes.class({'bg-red': hasError}).merge({type: 'button'}) }}>
{{ slot }}
</button>
[!NOTE]
If you need to conditionally compile classes on other HTML elements that shouldn’t receive merged attributes, you can use the@classdirective.
The attributes manager is a wrapper around the Ruby Hash class. Unless explicitly overwritten, any methods called on the attributes manager will call that same method on the underlying Hash.
You can filter attributes using the filter and slice methods. These methods call filter and slice on the underlying Hash and return a new attributes manager with the result.
{{ attributes.filter { |k, v| k == 'foo'} }}
{{ attributes.slice :foo }}
If you would like to check if an attribute is present on the component, you can use the has? method. This method accepts the attribute name as its only argument and returns a boolean indicating whether or not the attribute is present:
@if (attributes.has?(:class))
<div>Class attribute is present</div>
@endIf
If multiple parameters are passed to the has? method, the method will determine if all of the given attributes are present on the component:
@if (attributes.has?('name', 'class'))
<div>All of the attributes are present</div>
@endIf
The has_any? method can be used to determine if any of the given attributes are present on the component:
@if (attributes.has_any?('href', ':href', 'v-bind:href'))
<div>One of the attributes is present</div>
@endIf
You will often need to pass additional content to your component via “slots”. The default component slot is rendered by printing the slot variable. To explore this concept, let’s imagine that an alert component has the following markup:
{{-- /app/views/components/alert.rblade --}}
<div class="alert alert-danger">
{{ slot }}
</div>
We can pass content to the slot by injecting content into the component:
<x-alert>
<strong>Whoops!</strong> Something went wrong!
</x-alert>
[!NOTE]
You can instead use<//>as the closing tag of RBlade components; however, this will bypass some of the template sanity checking that the compiler performs.
Sometimes a component may need to render multiple different slots in different locations within the component. Let’s modify our alert component to allow for the injection of a “title” slot:
{{-- /app/views/components/alert.rblade --}}
@props(title: required)
<span class="alert-title">{{ title }}</span>
<div class="alert alert-danger">
{{ slot }}
</div>
You can define the content of the named slot using the x-slot tag. Any content not within an explicit x-slot tag will be passed to the component in the slot variable:
<x-alert>
<x-slot:title>
Server Error
</x-slot>
<strong>Whoops!</strong> Something went wrong!
</x-alert>
The slot object extends the String interface, so you can invoke a slot’s empty? method to determine if the slot contains content:
<span class="alert-title">{{ title }}</span>
<div class="alert alert-danger">
@if (slot.empty?)
This is default content if the slot is empty.
@else
{{ slot }}
@endIf
</div>
Like RBlade components, you can assign additional attributes to slots such as CSS class names:
<x-card class="shadow-sm">
<x-slot:heading class="font-bold">
Heading
</x-slot>
Content
<x-slot:footer class="text-sm">
Footer
</x-slot>
</x-card>
To interact with slot attributes, you can access the attributes property of the slot’s variable. For more information on how to interact with attributes, please consult the documentation on component attributes:
@props(
"heading": required,
"footer": required,
)
<div {{ attributes.class('border') }}>
<h1 {{ heading.attributes.class('text-lg') }}>
{{ heading }}
</h1>
{{ slot }}
<footer {{ footer.attributes.class('text-gray-700']) }}>
{{ footer }}
</footer>
</div>
Sometimes, you may wish to return early from a component without printing anything. For example, if you make an error component and no errors are passed in as properties, you might want to skip rendering. You can use the @shouldRender directive anywhere within a component to prevent the component from being rendered:
{{-- components/error.rblade --}}
@props(errors: [])
@shouldRender(errors.present?)
...
If you are building a package that utilizes RBlade components, or want to store your components elsewhere, you will need to manually register your component directory using the RBlade::ComponentStore.add_path method:
require "rblade/component_store"
# Auto-discover components in the app/components directory
RBlade::ComponentStore.add_path(Rails.root.join("app", "components"))
# Auto-discover components in the app/views/partials directory with the namespace "partial"
RBlade::ComponentStore.add_path(Rails.root.join("app", "views", "partials"), "partial")
If multiple directories are registered with the same namespace, RBlade will search for components in all the directories in the order they were registered.
Sometimes, when a component is made up of many RBlade templates, you may wish to group the given component’s templates within a single directory. For example, imagine an “accordion” component:
<x-accordion>
<x-accordion.item>
...
</x-accordion.item>
</x-accordion>
You could make these components with files in separate directories:
/app/views/components/accordion.rblade
/app/views/components/accordion/item.rblade
However, when an index.rblade template exists in a directory, it will be rendered when referring to that directory. So instead of having to have the “index” component in a separate app/views/components/accordion.rblade, we can group the components together:
/app/views/components/accordion/index.rblade
/app/views/components/accordion/item.rblade
The Rails params Hash is available in views and components. However, the @old directive is a useful shortcut that will output the old input value for a given key:
<input type="text" name="email" value="@old('email', user.email)">
The first parameter is the name of the previous input, and the second input is the default if the key isn’t present in params. The previous example is the equivalent of calling params.fetch:
<input type="text" name="email" value="{{ params.fetch(:email, user.email) }}">
Since HTML forms can’t make PUT, PATCH, or DELETE requests, you will need to add a hidden _method field to spoof these HTTP verbs. The @method RBlade directive can create this field for you:
<form action="/foo/bar" method="POST">
@method('PUT')
...
</form>
Alternatively, you can use the dedicated directives for each method: @put, @patch, or @delete.
RBlade allows you to push to named stacks which can be rendered elsewhere in another component. This can be particularly useful for specifying any JavaScript libraries required by your child views:
@push('scripts')
<script src="/example.js"></script>
@endPush
If you would like to @push content if a given boolean expression evaluates to true, you can use the @pushif directive:
@pushIf(shouldPush, 'scripts')
<script src="/example.js"></script>
@endPushIf
You can push to a stack as many times as needed. To render the complete stack contents, pass the name of the stack to the @stack directive:
<head>
<!-- Head Contents -->
@stack('scripts')
</head>
If you would like to prepend content onto the beginning of a stack, you should use the @prepend directive:
@push('scripts')
This will be second...
@endPush
// Later...
@prepend('scripts')
This will be first...
@endPrepend