Stimulus and Turbo (Hotwire) in Ruby on Rails - Performance & Optimization

Performance: Stimulus and Turbo (Hotwire)

MEDIUM IMPACT

This affects page load speed by reducing full page reloads and improves interaction responsiveness by updating only parts of the page.

Updating page content after user interaction without full reload

Ruby on Rails

<button data-action="click->controller#update">Update</button>

import { Controller } from '@hotwired/stimulus'
export default class extends Controller {
  update() {
    fetch('/partial_update')
      .then(response => response.text())
      .then(html => {
        this.element.outerHTML = html
      })
  }
}

Only updates the changed part of the page without full reload, reducing load and rendering cost.

📈 Performance Gainsingle reflow and repaint limited to updated element; avoids full page reload

Updating page content after user interaction without full reload

Ruby on Rails

document.querySelector('#button').addEventListener('click', () => { window.location.reload(); });

Reloading the entire page causes a full reload, blocking rendering and increasing load time.

📉 Performance Costblocks rendering for 500-1000ms depending on page size; triggers full reflow and repaint

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Full page reload on interaction	High (entire DOM replaced)	Multiple (full page)	High (full repaint)	[X] Bad
Turbo partial page update	Low (only changed fragments)	Single or few (targeted)	Low (partial repaint)	[OK] Good
Stimulus event-driven update	Low (targeted elements)	Single	Low	[OK] Good

Rendering Pipeline

Turbo intercepts navigation and form submissions to fetch HTML fragments, updating the DOM partially. Stimulus manages event-driven updates without full reloads, minimizing layout recalculations.

→Style Calculation

→Layout

→Paint

→Composite

⚠️ BottleneckLayout and Paint stages due to DOM updates

Core Web Vital Affected

LCP, INP

This affects page load speed by reducing full page reloads and improves interaction responsiveness by updating only parts of the page.

Optimization Tips

1Avoid full page reloads; use Turbo to update only changed HTML fragments.

2Use Stimulus to handle user interactions with minimal DOM updates.

3Target specific elements for updates to reduce layout recalculations and repaints.

Performance Quiz - 3 Questions

How does Turbo improve page load performance compared to full page reloads?

A By caching the entire page in the browser

B By fetching and updating only changed HTML fragments without full reload

C By disabling JavaScript during navigation

D By preloading all pages at once

DevTools: Performance

How to check: Record a session while interacting with the page. Look for long tasks and layout shifts during navigation or updates.

What to look for: Check for reduced long tasks and fewer layout recalculations indicating efficient partial updates.

Practice

1. What is the main purpose of Stimulus in a Rails application using Hotwire?

easy

A. To add simple JavaScript behavior to HTML elements using controllers and data attributes

B. To replace the entire page content on every user action

C. To handle database queries efficiently

D. To style HTML elements with CSS

Solution

1. Step 1: Understand Stimulus role

   Stimulus is designed to add JavaScript behavior to HTML by connecting controllers to elements via data attributes.

2. Step 2: Compare other options

   Replacing entire page content is Turbo's job, not Stimulus. Database queries and styling are unrelated.

3. Final Answer:

   To add simple JavaScript behavior to HTML elements using controllers and data attributes -> Option A

4. Quick Check:

   Stimulus = JavaScript behavior via controllers [OK]

Hint: Stimulus controls behavior, Turbo controls page updates [OK]

Common Mistakes:

• Confusing Turbo's page update role with Stimulus
• Thinking Stimulus handles styling or database
• Assuming Stimulus reloads full pages

2. Which of the following is the correct way to connect a Stimulus controller named hello to a button element?

easy

A. Click me

B. Click me

C. Click me

D. Click me

Solution

1. Step 1: Recall Stimulus controller connection syntax

   Stimulus controllers are connected using the data-controller attribute with the controller name.

2. Step 2: Verify other attributes

   data-action defines event handlers, data-target defines targets inside controllers, data-connect is invalid.

3. Final Answer:

   <button data-controller="hello">Click me</button> -> Option B

4. Quick Check:

   Controller connection uses data-controller [OK]

Hint: Use data-controller to link Stimulus controllers [OK]

Common Mistakes:

• Using data-action instead of data-controller to connect controller
• Confusing data-target with controller connection
• Using non-existent data-connect attribute

3. Given this Stimulus controller code:

export default class extends Controller {
  static targets = ["output"]
  greet() {
    this.outputTarget.textContent = "Hello, Stimulus!"
  }
}

and this HTML:

<div data-controller="greeting">
  <button data-action="click->greeting#greet">Say Hello</button>
  <span data-greeting-target="output"></span>
</div>

What happens when the button is clicked?

medium

A. The span text changes to 'Hello, Stimulus!'

B. Nothing happens because the controller name is wrong

C. The page reloads

D. An error is thrown because outputTarget is undefined

Solution

1. Step 1: Match controller and targets

   The controller is named 'greeting' and defines an output target. The HTML uses data-controller="greeting" and data-greeting-target="output" correctly.

2. Step 2: Understand the greet method and action

   The button triggers greet on click, which sets the outputTarget's textContent to 'Hello, Stimulus!'.

3. Final Answer:

   The span text changes to 'Hello, Stimulus!' -> Option A

4. Quick Check:

   Correct controller and target update text [OK]

Hint: Check controller name matches data-controller and targets [OK]

Common Mistakes:

• Mismatching controller name and data-controller attribute
• Forgetting to define static targets array
• Expecting page reload instead of DOM update

4. Identify the error in this Turbo Frame usage:

<turbo-frame id="messages">
  <%= render @messages %>
</turbo-frame>

When a new message is created, the frame does not update automatically. What is the likely cause?

medium

A. The frame id should be messages_frame instead of messages

B. Turbo Frames cannot render collections

C. The render call is missing a partial

D. The server response does not include a turbo-frame with matching id

Solution

1. Step 1: Understand Turbo Frame update mechanism

   Turbo Frames update only if the server response includes a turbo-frame element with the same id as the frame on the page.

2. Step 2: Identify the problem

   If the server response lacks a matching turbo-frame wrapper, Turbo cannot replace the frame content automatically.

3. Final Answer:

   The server response does not include a <turbo-frame> with matching id -> Option D

4. Quick Check:

   Matching turbo-frame id in response is required [OK]

Hint: Ensure server response wraps content in matching turbo-frame id [OK]

Common Mistakes:

• Changing frame id arbitrarily
• Assuming Turbo Frames can't render collections
• Forgetting to wrap response in turbo-frame tag

5. You want to create a live search feature using Turbo and Stimulus. Which approach correctly combines both to update search results as the user types without full page reload?

hard

A. Use Stimulus to reload the whole page manually on input change

B. Use Turbo Frames alone to reload the entire page on every keystroke

C. Use a Stimulus controller to listen for input events, send fetch requests to the server, and update a Turbo Frame with the results

D. Use Turbo Streams to replace the entire page content on input

Solution

1. Step 1: Understand live search requirements

   Live search updates results dynamically as the user types without full reload.

2. Step 2: Combine Stimulus and Turbo correctly

   Stimulus listens to input events and sends fetch requests. Turbo Frame updates only the results part of the page.

3. Step 3: Evaluate other options

   Reloading entire page on every keystroke is inefficient. Turbo Streams replace parts but need server push. Stimulus alone can't reload page efficiently.

4. Final Answer:

   Use a Stimulus controller to listen for input events, send fetch requests to the server, and update a Turbo Frame with the results -> Option C

5. Quick Check:

   Stimulus + Turbo Frame = dynamic partial updates [OK]

Hint: Stimulus handles events, Turbo Frame updates partial content [OK]

Common Mistakes:

• Reloading full page on every input
• Using Turbo Frames without Stimulus for input events
• Misusing Turbo Streams for full page replacement