Progressive enhancement in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a button that works without JavaScript.

Svelte

<button [1]>Click me</button>

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

Atype="button"

Bonclick="alert('Hi!')"

Cdisabled

Dhref="#"

Attempts:

3 left

💡 Hint

Common Mistakes

Using onclick attribute which requires JavaScript

Using href attribute on a button element

The type="button" attribute ensures the button behaves correctly without JavaScript.

2fill in blank

medium

Complete the Svelte code to show a message only if JavaScript is enabled.

Svelte

<noscript><p>Please enable JavaScript.</p></noscript>
{#if [1]
  <p>JavaScript is enabled!</p>
{/if}

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

Atrue

BjsEnabled

Cfalse

Dwindow

Attempts:

3 left

💡 Hint

Common Mistakes

Using variables that are undefined

Using false which never shows the message

Using true inside the {#if} block always shows the message when JavaScript runs.

3fill in blank

hard

Fix the error in this Svelte code to progressively enhance a form submit button.

Svelte

<form on:submit|[1]={handleSubmit}>
  <button type="submit">Send</button>
</form>

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

Aonce

BpreventDefault

Ccapture

DstopPropagation

Attempts:

3 left

💡 Hint

Common Mistakes

Using stopPropagation which only stops event bubbling

Using capture or once which do not prevent default

The preventDefault modifier stops the form from submitting normally, allowing JavaScript to handle it.

4fill in blank

hard

Fill both blanks to create a Svelte component that shows a message only after JavaScript loads.

Svelte

<script>
  let [1] = false;
  onMount(() => {
    [2] = true;
  });
</script>

{#if jsLoaded}
  <p>JavaScript is ready!</p>
{/if}

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

AjsLoaded

BisReady

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in declaration and assignment

Not setting the variable to true inside onMount

We declare jsLoaded as false, then set it to true inside onMount to show the message only after JS loads.

5fill in blank

hard

Fill all three blanks to create a Svelte form that works without JS and enhances with JS.

Svelte

<form method="POST" action="/submit" on:submit|[1]={handleSubmit}>
  <input name="email" type="email" required />
  <button type="submit">Submit</button>
</form>

<script>
  import { [2] } from 'svelte';
  let [3] = false;
  [2](() => {
    [3] = true;
  });
  function handleSubmit(event) {
    event.preventDefault();
    // handle form with JS
  }
</script>

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

ApreventDefault

BonMount

CjsReady

DstopPropagation

Attempts:

3 left

💡 Hint

Common Mistakes

Using stopPropagation instead of preventDefault

Not importing onMount

Using inconsistent variable names

The form uses preventDefault to stop normal submit when JS runs. We import onMount to detect JS load and set jsReady to true.

Practice

1. What is the main goal of progressive enhancement in Svelte applications?

easy

A. To load all data at once for faster performance

B. To use only JavaScript for all app functionality

C. To avoid using semantic HTML elements

D. To make sure the app works with basic features before adding advanced ones

Solution

1. Step 1: Understand the concept of progressive enhancement

   Progressive enhancement means starting with a simple, working version of the app that everyone can use.

2. Step 2: Identify the goal in Svelte apps

   In Svelte, this means building basic content first, then adding interactive features on top.

3. Final Answer:

   To make sure the app works with basic features before adding advanced ones -> Option D

4. Quick Check:

   Progressive enhancement = basic first, then advanced [OK]

Hint: Think: start simple, then add features [OK]

Common Mistakes:

• Assuming JavaScript must be used for everything
• Ignoring basic content for advanced features
• Skipping semantic HTML importance

2. Which of the following is the correct way to provide fallback content for users without JavaScript in a Svelte app?

easy

A. Enable JavaScript to see this app.

B.

C. No JS support

D. Enable JS

Solution

1. Step 1: Identify the HTML element for no-JavaScript fallback

   The tag is designed to show content only when JavaScript is disabled.

2. Step 2: Check the options for correct usage

   Enable JavaScript to see this app.

   uses correctly with fallback text. Others misuse tags or won't show fallback properly.

3. Final Answer:

   <noscript><p>Enable JavaScript to see this app.</p></noscript> -> Option A

4. Quick Check:

   Fallback for no JS = <noscript> [OK]

Hint: Use <noscript> for no-JS fallback content [OK]

Common Mistakes:

• Using <script> to detect JS absence
• Hiding fallback with CSS only
• Using <template> which doesn't render

3. Given this Svelte snippet for progressive enhancement:

<button aria-label="Toggle menu" on:click={toggleMenu}>Menu</button>
<nav class:open={menuOpen}>...</nav>

What happens if JavaScript is disabled in the browser?

medium

A. The menu is always visible because class binding works without JS

B. The button does nothing and the menu stays hidden

C. The button triggers toggleMenu even without JS

D. The menu is removed from the DOM

Solution

1. Step 1: Understand Svelte event handling and class binding

   The on:click event and class:open binding require JavaScript to work.

2. Step 2: Consider no JavaScript scenario

   Without JS, the button click does nothing and the class:open is not applied, so the menu stays hidden if initially hidden.

3. Final Answer:

   The button does nothing and the menu stays hidden -> Option B

4. Quick Check:

   JS off means no event or class binding [OK]

Hint: JS needed for event and class bindings [OK]

Common Mistakes:

• Thinking class binding works without JS
• Assuming button triggers function without JS
• Believing menu auto-shows without JS

4. You wrote this Svelte code for progressive enhancement:

<button on:click={toggle} aria-expanded={expanded}>Toggle</button>
<div hidden={!expanded}>Content</div>

But the content never shows when clicking the button. What is the likely problem?

medium

A. The hidden attribute does not toggle correctly with boolean binding

B. The aria-expanded attribute must be a string, not boolean

C. The toggle function is missing or not updating expanded

D. The on:click event is not supported in Svelte

Solution

1. Step 1: Check event and state connection

   The button's on:click calls toggle, which should update expanded state.

2. Step 2: Identify missing or broken toggle function

   If toggle is missing or doesn't update expanded, the hidden attribute never changes, so content stays hidden.

3. Final Answer:

   The toggle function is missing or not updating expanded -> Option C

4. Quick Check:

   Missing toggle function = no state change [OK]

Hint: Ensure toggle updates state variable [OK]

Common Mistakes:

• Thinking hidden attribute toggles automatically
• Confusing aria-expanded type requirements
• Believing on:click is unsupported in Svelte

5. You want to build a Svelte app that shows a list of items with a button to filter them. For progressive enhancement, which approach is best?

hard

A. Render the full list in HTML first, then use Svelte to filter items interactively

B. Render an empty list and fetch items only after JavaScript loads

C. Hide the list and show it only after the filter button is clicked

D. Use only JavaScript to create and display the list dynamically

Solution

1. Step 1: Understand progressive enhancement for lists

   Start with a fully rendered list in HTML so users without JS see all items.

2. Step 2: Add interactive filtering with Svelte

   Use Svelte to add filtering on top, enhancing the experience for JS users.

3. Final Answer:

   Render the full list in HTML first, then use Svelte to filter items interactively -> Option A

4. Quick Check:

   Basic content first, then interactive features [OK]

Hint: Show full content first, then add JS filters [OK]

Common Mistakes:

• Loading list only after JS runs
• Hiding content initially
• Relying solely on JS for content display