Development server and HMR in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the Svelte development server.

Svelte

npm run [1]

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

Astart

Btest

Cdev

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'build' instead of 'dev' to start the server.

Typing 'start' which is for production start, not development.

Running npm run dev starts the Svelte development server with hot module replacement.

2fill in blank

medium

Complete the code to import the Svelte component for hot reloading.

Svelte

import [1] from './App.svelte';

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

AApp

BComponent

CMain

DPage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic name like 'Component' instead of 'App'.

Using 'Main' or 'Page' which are not the default component names.

The main Svelte component is usually named App and imported from App.svelte.

3fill in blank

hard

Fix the error in the code to enable hot module replacement in Svelte.

Svelte

const app = new [1]({ target: document.body });

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

AComponent

BMain

CApplication

DApp

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong component name that is not imported.

Using a generic name like 'Component' which causes runtime errors.

The instance must be created from the imported App component to enable HMR.

4fill in blank

hard

Fill both blanks to create a Svelte app instance with hot module replacement support.

Svelte

const app = new [1]({ target: [2] });

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

AApp

Bdocument.body

Cdocument.getElementById('app')

DComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Component' instead of 'App' for the component name.

Using an invalid target like a string instead of a DOM element.

The app instance is created from App and attached to document.body for rendering.

5fill in blank

hard

Fill all three blanks to set up a Svelte app with hot module replacement and export it.

Svelte

import [1] from './App.svelte';

const app = new [2]({ target: [3] });

export default app;

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

AApp

Bdocument.body

Ddocument.getElementById('root')

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of component and target in the code.

Using a wrong DOM element for mounting.

Import and instantiate the App component, mount it to document.body, and export the app instance.

Practice

1. What is the main purpose of the development server in a Svelte project?

easy

A. To compile the app into a production build

B. To minify the app's JavaScript files

C. To deploy the app to a web server

D. To show your app live and update it as you code

Solution

1. Step 1: Understand the role of the development server

   The development server runs your app locally and shows live updates as you make changes.

2. Step 2: Differentiate from production tasks

   Compiling for production, deploying, and minifying are separate steps done after development.

3. Final Answer:

   To show your app live and update it as you code -> Option D

4. Quick Check:

   Development server = live updates [OK]

Hint: Development server = live preview while coding [OK]

Common Mistakes:

• Confusing development server with production build
• Thinking it deploys the app
• Assuming it minifies code automatically

2. Which command starts the Svelte development server with Hot Module Replacement (HMR)?

easy

A. npm run build

B. npm run dev

C. npm start

D. npm run serve

Solution

1. Step 1: Identify the standard Svelte dev command

   In Svelte projects, npm run dev starts the development server with HMR enabled.

2. Step 2: Understand other commands

   npm run build creates production files; npm start and npm run serve are not standard for Svelte dev server.

3. Final Answer:

   npm run dev -> Option B

4. Quick Check:

   Start dev server = npm run dev [OK]

Hint: Use npm run dev to start Svelte dev server with HMR [OK]

Common Mistakes:

• Using npm run build instead of dev
• Confusing npm start with npm run dev
• Trying npm run serve which is not default

3. Given this Svelte component running with HMR, what happens when you change the text inside the <p> tag and save the file?

medium

A. Nothing happens until you manually refresh the browser

B. The entire page reloads and the app state resets

C. Only the changed text updates instantly without full reload

D. The app crashes due to hot reload errors

Solution

1. Step 1: Understand Hot Module Replacement (HMR) behavior

   HMR updates only the changed parts of the app instantly without reloading the whole page.

2. Step 2: Apply to text change in <p> tag

   Changing text inside the paragraph triggers HMR to update that text immediately, preserving app state.

3. Final Answer:

   Only the changed text updates instantly without full reload -> Option C

4. Quick Check:

   HMR updates changed parts instantly [OK]

Hint: HMR updates only changed parts, no full reload [OK]

Common Mistakes:

• Thinking full page reload happens on every change
• Believing manual refresh is needed
• Assuming app crashes on text change

4. You run npm run dev but the browser does not update when you change your Svelte files. What is the most likely cause?

medium

A. The development server is not running or crashed

B. You forgot to save the file after editing

C. You used npm run build instead of npm run dev

D. Your browser cache is disabled

Solution

1. Step 1: Check if development server is active

   If the dev server is not running or crashed, no updates or HMR can happen.

2. Step 2: Evaluate other options

   Not saving files prevents changes but usually obvious; using build command doesn't start dev server; browser cache disabled does not stop updates.

3. Final Answer:

   The development server is not running or crashed -> Option A

4. Quick Check:

   Dev server running = updates work [OK]

Hint: Check if dev server is running when no updates appear [OK]

Common Mistakes:

• Assuming browser cache blocks updates
• Not saving files before expecting changes
• Confusing build command with dev server

5. You want to keep your app state while updating styles during development. Which feature of the Svelte development server helps you achieve this?

hard

A. Hot Module Replacement (HMR)

B. Full page reload on every change

C. Production build optimization

D. Manual browser refresh

Solution

1. Step 1: Understand state preservation during updates

   HMR updates only changed modules without reloading the whole page, preserving app state like variables and UI state.

2. Step 2: Contrast with other options

   Full reload resets state; production build is unrelated to live updates; manual refresh loses state.

3. Final Answer:

   Hot Module Replacement (HMR) -> Option A

4. Quick Check:

   Keep state during updates = HMR [OK]

Hint: HMR preserves app state during live updates [OK]

Common Mistakes:

• Thinking full reload keeps state
• Confusing production build with dev features
• Relying on manual refresh to keep state