Import maps (Rails 7+) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Stimulus library using import maps in Rails 7+.

Ruby on Rails

import { Application } from "@hotwired/[1]"

Drag options to blanks, or click blank then click option'

Awebpack

Bstimulus

Crails

Dturbo

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'turbo' instead of 'stimulus'.

Trying to import from 'rails' or 'webpack' which are incorrect here.

The Stimulus library is imported from "@hotwired/stimulus" using import maps in Rails 7+.

2fill in blank

medium

Complete the code to start the Stimulus application after importing it.

Ruby on Rails

const application = [1]()

Drag options to blanks, or click blank then click option'

Astart

Bnew Application

CApplication.start

DApplication

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start()' which is not a function here.

Trying 'new Application' which is not the correct syntax.

You create a new Stimulus application by calling the imported 'Application' as a function.

3fill in blank

hard

Fix the error in the import map tag in Rails HTML to include the correct attribute.

Ruby on Rails

<%= javascript_importmap_tags [1] %>

Drag options to blanks, or click blank then click option'

Adefer: true

Basync: true

Ctype: 'module'

Dsrc: 'application.js'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async: true' which is not supported here.

Adding 'type: module' manually which is handled automatically.

The 'javascript_importmap_tags' helper accepts the option 'defer: true' to defer script loading properly.

4fill in blank

hard

Fill both blanks to register a Stimulus controller named 'hello_controller' in the application.

Ruby on Rails

import HelloController from "./controllers/[1]"
application.[2]("hello", HelloController)

Drag options to blanks, or click blank then click option'

Aregister

Bhello_controller

Chello

Dcontrollers

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'controllers' instead of the controller file name.

Calling 'application.hello' instead of 'application.register'.

You import the controller file 'hello_controller' and register it with the application using 'register'.

5fill in blank

hard

Fill the blank to define an import map pin for 'chart.js' with preload in config/importmap.rb.

Ruby on Rails

pin "chart.js", to: "chart.umd.js", preload: [1]

Drag options to blanks, or click blank then click option'

A:vendor

B:cdn

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting preload to false disables preloading.

Using wrong symbols for 'under' or 'from' options.

To pin 'chart.js' with preload, set preload: true in importmap config.

Practice

1. What is the main purpose of using importmap in Rails 7+?

easy

A. To load JavaScript modules without needing a bundler

B. To compile Ruby code into JavaScript

C. To manage database migrations automatically

D. To style HTML elements with CSS

Solution

1. Step 1: Understand importmap's role in Rails 7+

   Import maps allow Rails apps to load JavaScript modules directly in the browser without bundling tools.

2. Step 2: Compare other options

   Options B, C, and D describe unrelated tasks: compiling Ruby, managing migrations, and styling, which are not importmap's purpose.

3. Final Answer:

   To load JavaScript modules without needing a bundler -> Option A

4. Quick Check:

   Import maps = load JS modules without bundler [OK]

Hint: Import maps = JS modules without bundler [OK]

Common Mistakes:

• Confusing importmap with asset bundlers
• Thinking importmap compiles Ruby code
• Mixing importmap with CSS or database tasks

2. Which command correctly registers a JavaScript module named chart.js using importmap in Rails?

easy

A. rails importmap add chart.js

B. bin/importmap pin chart.js

C. rails importmap pin chart.js

D. importmap pin chart.js

Solution

1. Step 1: Identify the correct command syntax

   The correct command to pin a module in Rails 7+ is bin/importmap pin [module].

2. Step 2: Check other options

   Options B, C, and D are incorrect: B uses an incorrect verb add, C uses invalid rails importmap pin, and D misses the bin/ prefix.

3. Final Answer:

   bin/importmap pin chart.js -> Option B

4. Quick Check:

   Pin module command = bin/importmap pin [name] [OK]

Hint: Use 'bin/importmap pin' to register modules [OK]

Common Mistakes:

• Using 'rails importmap' instead of 'bin/importmap'
• Using 'add' instead of 'pin'
• Omitting 'bin/' prefix in the command

3. Given this Rails view code snippet:

<%= javascript_importmap_tags %>

What does this helper do in a Rails 7+ app using import maps?

medium

A. It generates CSS styles for JavaScript components

B. It compiles JavaScript files into one bundle

C. It removes unused JavaScript from the app

D. It loads all pinned JavaScript modules into the HTML page

Solution

1. Step 1: Understand the helper's purpose

   javascript_importmap_tags inserts script tags to load all pinned JS modules via import maps in the HTML.

2. Step 2: Eliminate incorrect options

   It does not bundle, remove unused code, or generate CSS styles.

3. Final Answer:

   It loads all pinned JavaScript modules into the HTML page -> Option D

4. Quick Check:

   javascript_importmap_tags = load pinned JS modules [OK]

Hint: javascript_importmap_tags loads pinned JS modules [OK]

Common Mistakes:

• Thinking it bundles JS files
• Assuming it cleans unused code
• Confusing it with CSS helpers

4. You run rails importmap pin my_module but your JavaScript module does not load in the browser. What is the most likely mistake?

medium

A. You forgot to add <%= javascript_importmap_tags %> in your layout

B. You used pin instead of add command

C. You need to restart the Rails server after pinning

D. You must compile assets with webpack first

Solution

1. Step 1: Check how import maps load modules

   Pinning registers the module, but javascript_importmap_tags must be in the layout to load scripts.

2. Step 2: Review other options

   You used pin instead of add command is incorrect because pin is the right command. You need to restart the Rails server after pinning is unnecessary; no restart needed. You must compile assets with webpack first is wrong because import maps do not require webpack.

3. Final Answer:

   You forgot to add <%= javascript_importmap_tags %> in your layout -> Option A

4. Quick Check:

   Missing javascript_importmap_tags = no JS load [OK]

Hint: Add javascript_importmap_tags in layout to load modules [OK]

Common Mistakes:

• Not including javascript_importmap_tags in views
• Confusing pin with add command
• Thinking server restart is required
• Assuming webpack is needed with import maps

5. You want to use a third-party JavaScript library hosted on a CDN with import maps in Rails 7+. Which is the correct way to pin it in config/importmap.rb?

hard

A. pin 'library', from: 'https://cdn.example.com/library.js'

B. pin 'library', to: '/assets/library.js'

C. pin 'library', to: 'https://cdn.example.com/library.js'

D. pin 'library', url: 'https://cdn.example.com/library.js'

Solution

1. Step 1: Understand pin syntax for external URLs

   To pin a module from a CDN, use pin 'name', to: 'URL' in config/importmap.rb.

2. Step 2: Check other options

   pin 'library', to: '/assets/library.js' uses a local path, not CDN. Options C and D use incorrect keys from and url which are invalid.

3. Final Answer:

   pin 'library', to: 'https://cdn.example.com/library.js' -> Option C

4. Quick Check:

   Pin CDN module = pin 'name', to: 'URL' [OK]

Hint: Use 'to:' with CDN URL when pinning external modules [OK]

Common Mistakes:

• Using wrong keys like 'from' or 'url'
• Pinning local path instead of CDN URL
• Confusing syntax for pinning external scripts