Django Cotton

Bringing component-based design to Django templates.

• Docs site + demos: django-cotton.com

Contents

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

Why Cotton?

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.

Key Features

• 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.

Walkthrough

Your first component

<!-- 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.

Add attributes

<!-- 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

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>

Pass template variable as an attribute

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>

Template expressions inside attributes

You can use template expression statements inside attributes.

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

Boolean attributes

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>

Passing Python data types

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>

Increase Re-usability with {{ attrs }}

{{ 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 />

In-component Variables with <c-vars>

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:

1. Using <c-vars> for default attributes

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>

2. Using <c-vars> to govern {{ attrs }}

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" />

An example with HTMX

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>

Usage Basics

• 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

Limitations in Django that Cotton overcomes

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:

{% block %} and {% extends %}

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.

What about {% include %} ?

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.

What's with {% with %}?

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.

Custom {% templatetags %}

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]

Native Django template tags vs Cotton

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

HTML in attributes

❌ Django native:

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

✅ Cotton:

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

Template expressions in attributes

❌ Django native:

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

✅ Cotton:

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

Pass simple python types

❌ 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}" />

Multi-line definitions

❌ Django native:

{% my_component
    arg=1 %}

✅ Cotton:

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

Caching

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.

Changelog

Version	Date	Title and Description
v0.9.22	2024-07-19	We now scan all app directories for templates, as if APP_DIRS = True.
v0.9.21	2024-07-19	Fixed issue where '=' was breaking the attribute parsing by _component.
v0.9.20	2024-07-17	Set Charset from Engine Charset when processing template files should be utf-8 or as defined in the loader settings.
v0.9.19	2024-07-14	Fix: Cotton Loader Permits Duplicate Attributes in HTML Tags Fixed issue where the loader was not allowing Django template expressions to govern whole attributes inside HTML elements.
v0.9.18	2024-07-13	Fix: Allow Trailing/Leading Quotes in Attributes
v0.9.17	2024-07-11	Minor Cleanup
v0.9.16	2024-07-10	Cotton Component Caching Cotton components are now cached whilst in production / DEBUG = False. LRU cache type with a record count of 1024, cleared on app restart.
v0.9.15	2024-07-06	Hyphen to Underscore Conversion Converts variable names with hyphens to underscores for attribute access. i.e. <c-component x-data="{}" /> -> {{ x_data }}
v0.9.14	2024-07-05	c-vars Optimization Optimizes c-vars processing for performance, yielding a 15% speed improvement in component rendering.
v0.9.13	2024-07-05	Multi-line Attribute Support Enables multi-line values in attributes, allowing more support for js-expression style attributes like in alpine.js
v0.9.12	2024-07-03	Dropped ".cotton.html" Requirement Cotton no longer requires the .cotton.html suffix on component or view templates. A simple .html will do.
v0.9.11	2024-06-24	Attribute Ordering Fix Attribute ordering was not being kept during compilation which was breaking situations when using template expressions inside tags.
v0.9.10	2024-06-22	Template Expression Attributes Ensures that the new template expression attributes are also provided in {{ attrs }} alongside all normal attributes.
v0.9.9	2024-06-22	Native Tags in Attributes Cotton now allows you to include template variables inside attributes. Added expression attributes to {{ attrs }}.
v0.9.7	2024-06-21	Dynamic Type Attributes Using the : to prefix an attribute tells Cotton we're passing a dynamic type down. You can also send basic Python types.
v0.9.6	2024-06-17	Rename c-props to c-vars Rename c props, all <c-props /> are now <c-vars />.
v0.9.4	2024-06-11	Boolean Attributes Support for Boolean attributes added with docs update.
v0.9.1	2024-06-08	Open Source Release Open source release.

Comparison with other packages

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

Feature	Cotton	django-components	Slippers	Django Template Partials
Intro	UI-focused, expressive syntax	Holistic solution with backend logic	Enhances DTL for reusable components	Define and reuse inline HTML partials
Definition of ‘component’	An HTML template	A backend class with template	An HTML template	Inline specified partial
Syntax Style HTML-like	HTML-like	Django Template Tags	Django Template Tags with custom tags	Django Template Tags
Create component in one step?	Yes (place in folder)	No (create additional class file)	No (need to register in YAML file or with function)	Yes (declare inline or load via include tag)
Slots (default) Pass HTML content between tags	Yes	Yes	Yes	No
Named Slots Designate a slot in the component template	Yes	Yes	Yes, using ‘fragment’	No
Scoped Slots Reference component context in parent template	No	Yes	No	No
Dynamic Attributes Pass string literals of basic Python types	Yes	No	No	No
Boolean Attributes Pass valueless attributes as True	Yes	Yes	No	No
Declare Variables in Component View Set defaults for UI states	Yes	No (Use class properties)	Yes	No
Implicit Attribute Passing Pass all defined attributes to an element	Yes	No	Yes	No
Django Template Expressions in Attribute Values Use Django expressions in attribute values	Yes	No	No	No
Auto-Registering Components Start using components without manual registration	Yes	No (Create class with decorator)	No (Register in YAML file or with helper function)	Yes
Attribute Merging Replace existing attributes with component attributes	Yes	Yes	No	No
Multi-line Component Tags Write component tags over multiple lines	Yes	No	No	No