Stimulus

Stimulus is a modest JavaScript framework that connects JavaScript behavior to HTML via data attributes. It doesn't render HTML—it enhances existing HTML with interactivity.

1. HTML-First Philosophy

State lives in the DOM, not JavaScript. Controllers can be discarded between page changes and reinitialize from cached HTML. Design controllers to read state from data attributes and restore themselves on reconnection.

2. Convention Over Configuration

Stimulus uses predictable naming conventions:

• Controller: data-controller="clipboard"
• Targets: data-clipboard-target="source"
• Actions: data-action="click->clipboard#copy"
• Values: data-clipboard-url-value="/api/copy"
• Classes: data-clipboard-supported-class="visible"
• Outlets: data-clipboard-result-outlet="#result"

3. Lifecycle Awareness

Controllers have three lifecycle callbacks:

• initialize() - Called once when controller is instantiated
• connect() - Called when controller is connected to DOM (can happen multiple times with Turbo)
• disconnect() - Called when controller is removed from DOM

Always clean up in disconnect() what you set up in connect() (timers, event listeners, observers).

4. Scope Isolation

Each controller only sees elements within its scope (the element with data-controller and its descendants). Targets must be within scope. Use outlets to communicate across controller boundaries.

5. Progressive Enhancement

Build HTML that works without JavaScript first. Use Stimulus to enhance, not replace. Check for API support before using features:

connect() {
  if ("clipboard" in navigator) {
    this.element.classList.add(this.supportedClass)
  }
}

1. Build a new controller
2. Debug an existing controller
3. Add a feature to a controller
4. Review controller(s) for best practices
5. Optimize performance
6. Implement a UI pattern (modal, dropdown, tabs, etc.)
7. Integrate with Turbo
8. Handle forms
9. Something else

Wait for response before proceeding.

After reading the workflow, follow it exactly.

1. Does it connect? Check browser console for Stimulus connection messages
2. Do targets resolve? Verify this.hasXxxTarget returns true
3. Do actions fire? Add temporary console.log in action methods
4. Does it clean up? Navigate away and back - no errors, no memory leaks

// Debug mode - add to application.js
application.debug = true

Report to the user:

• "Controller connects: ✓"
• "Targets found: X of Y"
• "Actions working: ✓/✗"
• "Ready for testing"

All in references/:

Core APIs: architecture.md, targets.md, values.md, actions.md, outlets.md, classes.md Ecosystem: stimulus-use.md, ui-patterns.md Integration: turbo-integration.md Quality: testing-debugging.md, performance.md, anti-patterns.md

All in workflows/: