Stimulus and Turbo (Hotwire) in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Stimulus in the context of Hotwire?

Stimulus is a lightweight JavaScript framework that adds behavior to HTML by connecting controllers to elements. It helps you write small, reusable JavaScript pieces that respond to user actions without heavy frameworks.

beginner

What role does Turbo play in Hotwire?

Turbo speeds up web apps by replacing full page reloads with partial updates. It intercepts links and form submissions to update only parts of the page, making apps feel faster and smoother without writing much JavaScript.

beginner

How do Stimulus controllers connect to HTML elements?

Stimulus controllers connect using data attributes like data-controller on HTML elements. This tells Stimulus which controller to use, and you can add actions with data-action to respond to events like clicks.

intermediate

What is a Turbo Frame and how does it improve user experience?

A Turbo Frame is a part of the page that can update independently. When you click a link or submit a form inside a Turbo Frame, only that frame reloads, not the whole page. This makes interactions faster and smoother.

intermediate

How do Turbo Streams help update the page dynamically?

Turbo Streams let the server send small HTML snippets that tell the browser how to update parts of the page (like adding or removing elements) without a full reload. This keeps the page in sync with server changes in real time.

Which attribute connects a Stimulus controller to an HTML element?

A data-turbo

B data-frame

C data-action

D data-controller

The data-controller attribute tells Stimulus which controller to attach to the element.

What does Turbo primarily replace to make web apps faster?

A Full page reloads

B CSS stylesheets

C JavaScript event listeners

D Database queries

Turbo intercepts links and form submissions to avoid full page reloads, updating only parts of the page.

Which Hotwire component allows partial page updates by targeting specific page sections?

A Stimulus Controllers

B Turbo Frames

C Webpack

D Action Cable

Turbo Frames let you update only parts of the page independently, improving speed and user experience.

How do Turbo Streams update the page?

A By running JavaScript timers

B By reloading the entire page

C By sending HTML snippets with instructions to modify the DOM

D By changing CSS styles

Turbo Streams send small HTML fragments that tell the browser how to update parts of the page dynamically.

Which of these is NOT a feature of Stimulus?

A Handling server-side database queries

B Connecting controllers via data attributes

C Responding to user events

D Adding behavior to HTML elements

Stimulus is a JavaScript framework for client-side behavior; it does not handle server-side database queries.

Explain how Stimulus and Turbo work together to improve a Rails web app's user experience.

Think about how small JavaScript pieces and fast page updates combine.

Describe how you would use a Stimulus controller to respond to a button click in a Rails app using Hotwire.

Focus on connecting HTML attributes to controller methods.

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