Bringing component-based design to Django templates.

• Docs site + demos: django-cotton.com

Why?
Your First component
Attributes
Named Slots
Pass Template Variables
Template expressions in attributes
Boolean attributes
Passing Python data types
Increase Re-usability with {{ attrs }}
In-component Variables with <c-vars>
HTMX Example
Usage Basics
Limitations in Django that Cotton overcomes
Caching
Changelog
Comparison with other packages

Cotton aims to overcome certain limitations that exist in the django template system that hold us back when we want to apply modern practises to compose UIs in a modular and reusable way.

• Modern UI Composition: Efficiently compose and reuse UI components.
• Interoperable with Django: Cotton enhances django's existing template system.
• HTML-like Syntax: Better code editor support and productivity as component tags are similar to html tags.
• Minimal Overhead: Compiles to native Django components with dynamic caching.
• Encapsulates UI: Keep layout, design and interaction in one file (especially when paired with Tailwind and Alpine.js)
• Compliments HTMX: Create smart components, reducing repetition and enhancing maintainability.

<!-- cotton/button.html -->
<a href="/" class="...">{{ slot }}</a>

<!-- in view -->
<c-button>Contact</c-button>

<!-- html output -->
<a href="/" class="...">Contact</a>

Everything provided between the opening and closing tag is provided to the component as {{ slot }}. It can contain any content, HTML or Django template expression.

<!-- cotton/button.html -->
<a href="{{ url }}" class="...">
    {{ slot }}
</a>

<!-- in view -->
<c-button url="/contact">Contact</c-button>

<!-- html output -->
<a href="/contact" class="...">
    Contact
</a>

Named slots are a powerful concept. They allow us to provide HTML to appear in one or more areas in the component. Here we allow the button to optionally display an svg icon:

<!-- cotton/button.html -->
<a href="{{ url }}" class="...">
    {{ slot }}
  
    {% if icon %} 
        {{ icon }} 
    {% endif %}
</a>

<!-- in view -->
<c-button url="/contact">
    Contact
    <c-slot name="icon">
        <svg>...</svg>
    </c-slot>
</c-button>

Named slots can also contain any django native template logic:

<!-- in view -->
<c-button url="/contact">
    <c-slot name="icon">
      {% if mode == 'edit' %}
          <svg id="pencil">...</svg>
      {% else %}
          <svg id="disk">...</svg>
      {% endif %}
    </c-slot>
</c-button>

To pass a template variable you prepend the attribute name with a colon :. Consider a bio card component:

<!-- in view -->
<c-bio-card :user="user" />

That has a component definition like:

<!-- cotton/bio_card.html -->
<div class="...">
  <img src="{{ user.avatar }}" alt="...">
  {{ user.username }} {{ user.country_code }}
</div>

You can use template expression statements inside attributes.

<c-weather icon="fa-{{ icon }}"
           unit="{{ unit|default:'c' }}"
           condition="very {% get_intensity %}"
/>

Boolean attributes reduce boilerplate when we just want to indicate a certain attribute should be True or not.

<!-- in view -->
<c-button url="/contact" external>Contact</c-button>

By passing just the attribute name without a value, it will automatically be provided to the component as True

<!-- cotton/button.html -->
<a href="{{ url }}" {% if external %} target="_blank" {% endif %} class="...">
    {{ slot }}
</a>

Using the ':' to prefix an attribute tells Cotton we're passing a dynamic type down. We already know we can use this to send a variable, but you can also send basic python types, namely:

• Integers and Floats
• None, True and False
• Lists
• Dictionaries

This benefits a number of use-cases, for example if you have a select component that you want to provide the possible options from the parent:

<!-- cotton/select.html -->
<select {{ attrs }}>
    {% for option in options %}
        <option value="{{ option }}">{{ option }}</option>
    {% endfor %}
</select>

<c-select name="q1" :options="['yes', 'no', 'maybe']" />

<!-- source code output -->
<select name="q1">
    <option value="yes">yes</option>
    <option value="no">no</option>
    <option value="maybe">maybe</option>
</select>

{{ attrs }} is a special variable that contains all the attributes passed to the component in an key="value" format. This is useful when you want to pass all attributes to a child element without having to explicitly define them in the component template. For example, you have inputs that can have any number of attributes defined:

<!-- cotton/input.html -->
<input type="text" class="..." {{ attrs }} />

<!-- example usage -->
<c-input placeholder="Enter your name" />
<c-input name="country" id="country" value="Japan" />
<c-input class="highlighted" required />

<!-- html output -->
<input type="text" class="..." placeholder="Enter your name" />
<input type="text" class="..." name="country" id="country" value="Japan" />
<input type="text" class="..." class="highlighted" required />

Django templates adhere quite strictly to the MVC model and does not permit a lot of data manipulation in views. Fair enough, but what if we want to handle data for the purpose of UI state only? Having presentation related variables defined in the back is overkill and can quickly lead to higher maintenance cost and loses encapsulation of the component. Cotton allows you define in-component variables for the following reasons:

In this example we have a button component with a default "theme" but it can be overridden.

<!-- cotton/button.html -->
<c-vars theme="bg-purple-500" />

<a href="..." class="{{ theme }}">
    {{ slot }}
</a>

<!-- in view -->
<c-button>I'm a purple button</c-button>

<!-- html output -->
<a href="..." class="bg-purple-500">
    I'm a purple button
</a>

Now we have a default theme for our button, but it is overridable:

<!-- in view -->
<c-button theme="bg-green-500">But I'm green</c-button>

<!-- html output -->
<a href="..." class="bg-green-500">
    But I'm green
</a>

Using {{ attrs }} to pass all attributes from parent scope onto an element in the component, you'll sometimes want to provide additional properties to the component which are not intended to be an attributes. In this case you can declare them in <c-vars /> and it will prevent it from being in {{ attrs }}

Take this example where we want to provide any number of attributes to an input but also an icon setting which is not intened to be an attribute on <input>:

<!-- in view -->
<c-input type="password" id="password" icon="padlock" />

<!-- cotton/input.html -->
<c-vars icon />

<img src="icons/{{ icon }}.png" />

<input {{ attrs }} />

Input will have all attributes provided apart from the icon:

<input type="password" id="password" />

Cotton helps carve out re-usable components, here we show how to make a re-usable form, reducing code repetition and improving maintainability:

<!-- cotton/form.html -->
<div id="result" class="..."></div>

<form {{ attrs }} hx-target="#result" hx-swap="outerHTML">
    {{ slot }}
    <button type="submit">Submit</button>
</form>

<!-- in view -->
<c-form hx-post="/contact">
    <input type="text" name="name" placeholder="Name" />
    <input type="text" name="email" placeholder="Email" />
    <input type="checkbox" name="signup" />
</c-form>

<c-form hx-post="/buy">
    <input type="text" name="type" />
    <input type="text" name="quantity" />
</c-form>

• Component Placement: Components should be placed in the templates/cotton folder.
• Naming Conventions:
  • Component filenames use snake_case: my_component.html
  • Components are called using kebab-case: <c-my-component />

For full docs and demos, checkout django-cotton.com

Whilst you can build frontends with Django’s native tags, there are a few things that hold us back when we want to apply modern practices:

This system strongly couples child and parent templates making it hard to create a truly re-usable component that can be used in places without it having a related base template.

Modern libraries allow components to be highly configurable, whether it’s by attributes, passing variables, passing HTML with default and named slots. {% include %} tags, whilst they have the ability to pass simple variables and text, they will not allow you to easily send HTML blocks with template expressions let alone other niceties such as boolean attributes, named slots etc.

Whilst {% with %} tags allow us to provide variables and strings it quickly busies up your code and has the same limitations about passing more complex types.

Cotton does essentially compile down to templatetags but there is some extra work it performs above it to help with scoping and auto-managing keys which will be difficult to manage manually in complex nested structures.

[Source article]

In addition, Cotton enables you to navigate around some of the limitations with Django's native tags and template language:

❌ Django native:

{% my_component header="<h1>Header</h1>" %}

✅ Cotton:

<c-my-component>
    <c-slot name="header">
        <h1>Header</h1>
    </c-slot>
</c-my-component>

❌ Django native:

{% my_component model="todos.{{ index }}.name" extra="{% get_extra %}" %}

✅ Cotton:

<c-my-component model="todos.{{ index }}.name" extra="{% get_extra %} />

❌ Django native:

{% my_component default_options="['yes', 'no', 'maybe']" %}
{% my_component config="{'open': True}" %}

✅ Cotton:

<c-my-component :default_options="['yes', 'no', 'maybe']" />
<c-my-component :config="{'open': True}" />

❌ Django native:

{% my_component
    arg=1 %}

✅ Cotton:

<c-my-component
    class="blue"
    x-data="{
        something: 1
    }" />

Cotton components are cached whilst in production (DEBUG = False). The cache's TTL is for the duration of your app's lifetime. So on deployment, when the app is normally restarted, caches are cleared. During development, changes are detected on every component render. This feature is a work in progress and some refinement is planned.

Note: For mistakes or if I have missed something from other packages - please create an issue!