Webpacker and JavaScript bundling in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import a JavaScript module using Webpacker in Rails.

Ruby on Rails

import [1] from 'components/button';

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

AButton

Bbutton

Cbtn

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for imported components

Using generic names like 'Component'

You import the module by its exported name, which is usually capitalized like Button.

2fill in blank

medium

Complete the code to add a JavaScript pack tag in a Rails view.

Ruby on Rails

<%= javascript_pack_tag '[1]' %>

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

Aapp

Bmain

Cbundle

Dapplication

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect pack names like 'app' or 'bundle'

Omitting quotes around the pack name

The default pack file is named application, so you include it with javascript_pack_tag 'application'.

3fill in blank

hard

Fix the error in the Webpacker config to enable source maps.

Ruby on Rails

[1].devtool = 'source-map';
module.exports = [1];

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

Aenvironment

Bwebpack

Cconfig

Dmerge

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'merge' or 'webpack' instead of 'environment'

Not exporting the correct config object

The Webpacker config uses environment to customize settings like source maps.

4fill in blank

hard

Fill both blanks to create a Webpack alias for easier imports.

Ruby on Rails

environment.config.[1].alias = {
  '@components': path.[2](__dirname, '../../app/javascript/components')
};

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

Aresolve

Bjoin

CresolvePath

DpathJoin

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like 'resolvePath'

Using 'pathJoin' which is not a function

You set aliases under resolve.alias and use path.join to build paths.

5fill in blank

hard

Fill all three blanks to configure Babel loader in Webpacker.

Ruby on Rails

environment.loaders.append('babel', {
  test: /\.js$/,
  exclude: /node_modules/,
  use: {
    loader: '[1]',
    options: {
      presets: [ '[2]' ],
      plugins: [ '[3]' ]
    }
  }
});

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

Ababel-loader

B@babel/preset-env

C@babel/plugin-transform-runtime

Dwebpack-loader

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong loader names like 'webpack-loader'

Confusing presets and plugins

The Babel loader is called babel-loader. The preset @babel/preset-env compiles modern JS, and the plugin @babel/plugin-transform-runtime optimizes helper code.

Practice

1. What is the main purpose of Webpacker in a Rails application?

easy

A. To style HTML elements with CSS

B. To bundle JavaScript files so they load efficiently in the browser

C. To manage database migrations automatically

D. To handle user authentication

Solution

1. Step 1: Understand Webpacker's role

   Webpacker is designed to bundle JavaScript files for Rails apps.

2. Step 2: Identify its main function

   Bundling means combining files to load faster and more efficiently in browsers.

3. Final Answer:

   To bundle JavaScript files so they load efficiently in the browser -> Option B

4. Quick Check:

   Webpacker bundles JS = C [OK]

Hint: Webpacker bundles JS files for faster loading [OK]

Common Mistakes:

• Confusing Webpacker with database tools
• Thinking Webpacker styles HTML
• Assuming Webpacker manages user login

2. Which of the following is the correct way to include a Webpacker JavaScript pack in a Rails view?

easy

A. <%= javascript_pack_tag 'application' %>

B. <%= stylesheet_pack_tag 'application' %>

C. <%= javascript_include_tag 'application.js' %>

D. <%= image_pack_tag 'application' %>

Solution

1. Step 1: Identify the helper for JS packs

   Webpacker uses javascript_pack_tag to include JS bundles.

2. Step 2: Confirm correct syntax

   The syntax is <%= javascript_pack_tag 'pack_name' %>, so <%= javascript_pack_tag 'application' %> matches.

3. Final Answer:

   <%= javascript_pack_tag 'application' %> -> Option A

4. Quick Check:

   Use javascript_pack_tag for JS packs = A [OK]

Hint: Use javascript_pack_tag to load JS bundles in views [OK]

Common Mistakes:

• Using stylesheet_pack_tag for JavaScript
• Using javascript_include_tag instead of javascript_pack_tag
• Confusing image_pack_tag with JS inclusion

3. Given the following JavaScript pack file app/javascript/packs/hello.js with content:

import { greet } from '../utils/greet'
console.log(greet('Rails'))

and app/javascript/utils/greet.js contains:

export function greet(name) {
  return `Hello, ${name}!`
}

What will be printed in the browser console when the pack is loaded?

medium

A. SyntaxError: Unexpected token

B. greet is not defined

C. Hello, undefined!

D. Hello, Rails!

Solution

1. Step 1: Understand the import and export

   The greet function is exported from utils/greet.js and imported correctly in hello.js.

2. Step 2: Analyze the console.log output

   Calling greet('Rails') returns the string Hello, Rails!, which is logged.

3. Final Answer:

   Hello, Rails! -> Option D

4. Quick Check:

   Correct import/export logs greeting = D [OK]

Hint: Check import/export paths and function calls for output [OK]

Common Mistakes:

• Forgetting to export the function
• Using wrong import path
• Expecting undefined instead of correct string

4. You added a new JavaScript file app/javascript/packs/custom.js but when you include it with <%= javascript_pack_tag 'custom' %>, the browser console shows a 404 error. What is the most likely cause?

medium

A. You forgot to restart the Rails server after adding the pack

B. The file is not saved in the correct directory

C. The javascript_pack_tag helper is deprecated and should not be used

D. The file has syntax errors preventing compilation

Solution

1. Step 1: Check file location

   The file is correctly placed in app/javascript/packs/, so location is likely correct.

2. Step 2: Consider server restart

   Webpacker requires the Rails server or webpack-dev-server to restart to detect new packs.

3. Final Answer:

   You forgot to restart the Rails server after adding the pack -> Option A

4. Quick Check:

   Restart server to load new packs = A [OK]

Hint: Restart server after adding new JS packs [OK]

Common Mistakes:

• Assuming helper is deprecated
• Ignoring server restart requirement
• Blaming syntax errors without checking logs

5. You want to organize your JavaScript code by creating a module app/javascript/modules/calc.js exporting a function add(a, b). How should you import and use this function in your pack file app/javascript/packs/main.js to log the sum of 5 and 7?

hard

A. import add from '../modules/calc.js'
console.log(add(5, 7))

B. require('../modules/calc')
console.log(add(5, 7))

C. import { add } from '../modules/calc'
console.log(add(5, 7))

D. import * as calc from '../modules/calc'
console.log(calc.add(5, 7))

Solution

1. Step 1: Understand ES module import syntax

   If add is a named export, import it with curly braces: import { add } from 'path'.

2. Step 2: Use the function correctly

   Call add(5, 7) and log the result with console.log.

3. Final Answer:

   import { add } from '../modules/calc' console.log(add(5, 7)) -> Option C

4. Quick Check:

   Named export import uses braces = B [OK]

Hint: Use curly braces to import named exports [OK]

Common Mistakes:

• Using default import syntax for named exports
• Using require instead of import in Webpacker
• Forgetting to call function from imported module