Progressive enhancement in Svelte - Mini Project: Build & Apply

Progressive Enhancement with Svelte

📖 Scenario: You are building a simple web page that shows a list of favorite fruits. You want the page to work well even if JavaScript is disabled, but also enhance the experience when JavaScript is available.

🎯 Goal: Create a Svelte component that displays a list of fruits using basic HTML first, then progressively enhance it by adding a filter input that lets users search fruits dynamically.

📋 What You'll Learn

Create a list of fruits in the component

Add a text input to filter fruits by name

Use Svelte reactive statements to update the filtered list

Ensure the list is visible and usable without JavaScript

💡 Why This Matters

🌍 Real World

Many websites need to work well even if users disable JavaScript or have slow connections. Progressive enhancement ensures basic content is always accessible and improves the experience when JavaScript is available.

💼 Career

Understanding progressive enhancement is important for front-end developers to build accessible, robust web applications that work for all users.

1

Create the initial fruit list

Create a Svelte component with a variable called fruits that is an array containing these exact strings: "Apple", "Banana", "Cherry", "Date", and "Elderberry". Then, add an unordered list <ul> in the markup that uses {#each fruits as fruit} to display each fruit inside a <li>.

Svelte

  // Your code here



  

Hint

Start by declaring the fruits array inside a <script> tag. Then use Svelte's {#each} block to loop through the array and display each fruit in a list item.

2

Add a filter input variable

Add a variable called filter initialized to an empty string "" inside the <script> tag. Then add a text input <input type="text" bind:value={filter} placeholder="Filter fruits" /> above the list in the markup.

Svelte

  let fruits = ["Apple", "Banana", "Cherry", "Date", "Elderberry"];
  // Your code here




  {#each fruits as fruit}
    {fruit}
  {/each}

Hint

Declare the filter variable in the script. Then add an input element with bind:value={filter} so it updates as the user types.

3

Filter the fruit list reactively

Add a reactive statement $: filteredFruits = fruits.filter(fruit => fruit.toLowerCase().includes(filter.toLowerCase())) inside the <script> tag. Then update the {#each} block to loop over filteredFruits instead of fruits.

Svelte

  let fruits = ["Apple", "Banana", "Cherry", "Date", "Elderberry"];
  let filter = "";
  // Add reactive filteredFruits here





  {#each filteredFruits as fruit}
    {fruit}
  {/each}

Hint

Use a reactive statement starting with $: to create filteredFruits based on the current filter. Then loop over filteredFruits in the markup.

4

Add a <noscript> message for no JavaScript

Add a <noscript> tag below the input that contains a paragraph <p> with the exact text: JavaScript is disabled. You see the full fruit list.. This message will show only if JavaScript is disabled, enhancing accessibility.

Svelte

  let fruits = ["Apple", "Banana", "Cherry", "Date", "Elderberry"];
  let filter = "";
  $: filteredFruits = fruits.filter(fruit => fruit.toLowerCase().includes(filter.toLowerCase()));







  {#each filteredFruits as fruit}
    {fruit}
  {/each}

Hint

Use the <noscript> tag to show a message only when JavaScript is off. Put a paragraph inside with the exact text.

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