dialog-patterns（dialog 模式）

Native Dialog Patterns for Rails

Build accessible, modern dialog UIs using the native HTML <dialog> element with Turbo Frames and Stimulus. No JavaScript frameworks or heavy libraries required.

When to Use This Skill

• Building modal dialogs for forms, confirmations, or content
• Creating toast/alert notifications
• Implementing confirmation dialogs (delete, destructive actions)
• Any overlay UI that needs focus management and accessibility

Why Native <dialog>?

Zero-JavaScript Confirmation Dialogs (Recommended)

Modern browsers support the Invoker Commands API for declarative dialog control—no JavaScript required. See references/zero-js-patterns.md for complete examples.

Quick Reference

<%= button_tag "Delete", commandfor: "delete-#{post.id}", command: "show-modal" %>

<dialog id="delete-<%= post.id %>" closedby="any" role="alertdialog">
  <h3>Delete "<%= post.title %>"?</h3>
  <button commandfor="delete-<%= post.id %>" command="close">Cancel</button>
  <%= button_to "Delete", post, method: :delete %>
</dialog>

Key Attributes

When to Use Zero-JS vs Stimulus

Additional Patterns (see references/)

• CSS animations with @starting-style for enter/exit transitions
• Turbo.config.forms.confirm to replace ugly browser dialogs
• Progressive enhancement for cross-browser compatibility

Core Pattern: Async Modal with Turbo Frames

The recommended pattern for Rails modals combines three technologies:

1. Turbo Frame - Async content loading without page reload
2. Native <dialog> - Accessible modal presentation
3. Stimulus controller - Lifecycle management

Step 1: Layout Container

Add a modal turbo-frame to your layout:

<%# app/views/layouts/application.html.erb %>
<body>
  <%= yield %>

  <%# Modal injection point %>
  <%= turbo_frame_tag :modal %>
</body>

Step 2: Trigger Links

Target the modal frame from any link:

<%# Any view %>
<%= link_to "New Post", new_post_path, data: { turbo_frame: :modal } %>
<%= link_to "Edit", edit_post_path(@post), data: { turbo_frame: :modal } %>
<%= link_to "Confirm Delete", confirm_delete_post_path(@post), data: { turbo_frame: :modal } %>

Step 3: Modal Content View

Wrap modal content in matching turbo-frame with nested inner frame:

<%# app/views/posts/new.html.erb %>
<%= turbo_frame_tag :modal do %>
  <%# Inner frame prevents flash during form validation %>
  <%= turbo_frame_tag :modal_content do %>
    <dialog data-controller="dialog" data-action="click->dialog#clickOutside" open>
      <article>
        <header>
          <h2>New Post</h2>
          <button data-action="dialog#close" aria-label="Close">&times;</button>
        </header>

        <%= render "form", post: @post %>
      </article>
    </dialog>
  <% end %>
<% end %>

Step 4: Stimulus Controller

Key behaviors: showModal() on connect, replaceChildren() on disconnect (prevents stale content), clickOutside for backdrop close.

See references/dialog-examples.md for full Stimulus controller, CSS styling, and Tailwind variant.

Why Nested Turbo Frames?

The nested frame pattern (modal > modal_content) prevents content flashing:

<%= turbo_frame_tag :modal do %>
  <%= turbo_frame_tag :modal_content do %>
    <dialog>...</dialog>
  <% end %>
<% end %>

Problem without nested frame: When a form inside the modal has validation errors and re-renders, the outer frame briefly shows the old content before replacing it.

Solution with nested frame: The inner frame handles form re-renders independently, keeping the modal structure stable.

Form Handling in Modals

Successful Submission

Redirect with Turbo to close modal and update page:

# app/controllers/posts_controller.rb
def create
  @post = Post.new(post_params)

  if @post.save
    redirect_to posts_path, notice: "Post created!"
  else
    render :new, status: :unprocessable_entity
  end
end

The redirect navigates _top (full page), effectively closing the modal.

Validation Errors

Re-render the form with 422 status to keep modal open:

render :new, status: :unprocessable_entity

Turbo Stream Response (Stay in Modal)

Use turbo_stream.update("modal", "") to clear modal without full redirect. See references/dialog-examples.md for full example.

Confirmation Dialog Pattern

For destructive actions: add a confirm_delete member route, render a dialog in a turbo frame, trigger via link_to with data: {turbo_frame::modal}.

See references/dialog-examples.md for full confirmation dialog view, route, and trigger.

Alert/Toast Pattern

For flash messages and notifications. Use show() instead of showModal() for non-modal presentation. See references/toast-slideover-patterns.md for complete implementation.

<dialog class="toast" data-controller="toast" data-toast-duration-value="5000">
  <p><%= message %></p>
</dialog>

Key difference: show() opens without backdrop or focus trap (toasts), showModal() centers with backdrop (modals).

Slideover Panel Pattern

For side panels (settings, filters, details). See references/toast-slideover-patterns.md for styling and animations.

<dialog class="slideover" data-controller="dialog" data-action="click->dialog#clickOutside">
  <aside>
    <header><h2>Filters</h2></header>
    <%= render "filters" %>
  </aside>
</dialog>

Accessibility

Native <dialog> provides focus trapping, ESC close, background inert, and top layer automatically. Additionally ensure:

• Visible close button (not just ESC)
• aria-labelledby / aria-describedby for descriptive context
• Focus return to trigger element on close (store document.activeElement in connect())

See references/dialog-examples.md for enhanced accessibility and focus return examples.

Common Patterns Summary

Anti-Patterns to Avoid

Testing Dialogs

# System test - use `within "dialog"` to scope assertions
within "dialog" do
  fill_in "Title", with: "My Post"
  click_button "Create"
end
expect(page).not_to have_selector("dialog[open]")  # Modal closed

Browser Support

For older browsers: dialog polyfill, invokers polyfill. See references/zero-js-patterns.md for progressive enhancement strategies.