Islands architecture in Fresh in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Island component correctly in Fresh.

Deno

import [1] from "./components/Counter.tsx";

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

Aisland

BIsland

CComponent

Dcounter

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for component imports.

Importing with a different name than exported.

The Island component must be imported with the exact name used in the component file, which is usually Island.

2fill in blank

medium

Complete the code to mark the component as an Island in Fresh.

Deno

export default [1](Counter);

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

AwithIsland

BwithIslandClient

CwithIslandServer

DwithIslandClientOnly

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect wrapper functions like withIslandClient or withIslandServer.

Not wrapping the component at all.

The withIsland function wraps the component to mark it as an Island in Fresh.

3fill in blank

hard

Fix the error in the Island component usage by completing the attribute to hydrate the Island.

Deno

<Counter [1] />

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

Aclient:media

Bclient:idle

Cclient:load

Dclient:visible

Attempts:

3 left

💡 Hint

Common Mistakes

Using client:idle or client:visible which delay hydration.

Forgetting to add any client hydration attribute.

The client:load attribute tells Fresh to hydrate the Island immediately after the page loads.

4fill in blank

hard

Fill both blanks to create a simple Island component with state and event handler.

Deno

const [count, [1]] = useState(0);

<button onClick=[2](() => setCount(count + 1))>Click</button>

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

AsetCount

BuseCallback

CuseEffect

Dincrement

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong function names for state updater.

Not wrapping the event handler with useCallback.

setCount updates the state, and useCallback memoizes the click handler for performance.

5fill in blank

hard

Fill all three blanks to complete the Island component export with client hydration and import.

Deno

import [1] from "preact/hooks";
import Counter from "./Counter.tsx";

export default [2](Counter, { [3]: true });

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

AuseState

BwithIsland

Cclient:load

DuseEffect

Attempts:

3 left

💡 Hint

Common Mistakes

Importing wrong hooks.

Not using withIsland to export.

Missing client hydration option.

We import useState hook, wrap the component with withIsland, and enable client:load hydration.

Practice

1. What is the main purpose of the Islands architecture in Fresh?

easy

A. To split pages into static and interactive parts for better performance

B. To make all parts of the page fully interactive

C. To load the entire page on the client side only

D. To disable JavaScript on the page

Solution

1. Step 1: Understand Islands architecture concept

   Islands architecture divides a web page into static parts and small interactive components called islands.

2. Step 2: Identify the main benefit

   This split improves page speed and maintainability by only hydrating interactive parts.

3. Final Answer:

   To split pages into static and interactive parts for better performance -> Option A

4. Quick Check:

   Islands architecture = split static + interactive [OK]

Hint: Islands means splitting page into static and interactive parts [OK]

Common Mistakes:

• Thinking all page parts are interactive
• Believing Islands disables JavaScript
• Assuming full client-side rendering

2. Which syntax correctly marks an interactive island component in Fresh?

easy

A. <ISLAND>MyComponent</ISLAND>

B. <Island>MyComponent</Island>

C. <island>MyComponent</island>

D. <ISLAND />

Solution

1. Step 1: Recall correct tag casing

   Fresh uses uppercase ISLAND tag to mark interactive components.

2. Step 2: Check tag usage

   The ISLAND tag wraps the component, so it needs opening and closing tags.

3. Final Answer:

   <ISLAND>MyComponent</ISLAND> -> Option A

4. Quick Check:

   Correct tag is uppercase ISLAND with open/close [OK]

Hint: Use uppercase <ISLAND> tags to mark interactive parts [OK]

Common Mistakes:

• Using lowercase or mixed case tags
• Using self-closing without children
• Confusing with other component tags

3. Given this Fresh page snippet, what will be interactive on the rendered page?

export default function Page() {
  return (
    <main>
      <h1>Welcome</h1>
      <ISLAND><Counter /></ISLAND>
      <p>Static text</p>
    </main>
  );
}

medium

A. Nothing is interactive because ISLAND is not a valid tag

B. The entire page including the heading and paragraph is interactive

C. Only the Counter component inside the ISLAND tag is interactive

D. Only the heading is interactive

Solution

1. Step 1: Identify ISLAND usage

   The Counter component is wrapped inside the ISLAND tag, marking it interactive.

2. Step 2: Understand static vs interactive parts

   The heading and paragraph are outside ISLAND, so they remain static and non-interactive.

3. Final Answer:

   Only the Counter component inside the ISLAND tag is interactive -> Option C

4. Quick Check:

   ISLAND wraps interactive parts only [OK]

Hint: Only components inside <ISLAND> are interactive [OK]

Common Mistakes:

• Assuming whole page is interactive
• Thinking ISLAND tag is invalid
• Believing static parts become interactive

4. What is wrong with this Fresh island component usage?

export default function Page() {
  return (
    <main>
      <ISLAND><Button /></ISLAND>
      <ISLAND><Button /></ISLAND>
    </main>
  );
}

medium

A. ISLAND tags must be self-closing

B. Using multiple ISLAND tags with the same component can cause duplicate hydration issues

C. Button component cannot be used inside ISLAND

D. ISLAND tags must wrap only one element, not components

Solution

1. Step 1: Analyze multiple ISLAND usage

   Using the same interactive component multiple times inside separate ISLAND tags can cause hydration conflicts if keys are missing.

2. Step 2: Understand hydration uniqueness

   Each island needs a unique key or identifier to avoid duplicate hydration errors.

3. Final Answer:

   Using multiple ISLAND tags with the same component can cause duplicate hydration issues -> Option B

4. Quick Check:

   Duplicate islands need unique keys to avoid errors [OK]

Hint: Multiple identical islands need unique keys to avoid errors [OK]

Common Mistakes:

• Thinking ISLAND tags must be self-closing
• Believing components can't be inside ISLAND
• Assuming ISLAND wraps only HTML elements

5. You want to optimize a Fresh page with many interactive buttons. Which approach best uses Islands architecture to improve performance?

hard

A. Use <ISLAND> tags only on static content to reduce JavaScript

B. Wrap all buttons together in a single <ISLAND> to hydrate them all at once

C. Do not use <ISLAND> tags and hydrate the entire page client-side

D. Wrap each button in its own <ISLAND> with unique keys to hydrate only needed parts

Solution

1. Step 1: Understand hydration granularity

   Wrapping each button in its own ISLAND allows independent hydration, improving performance by loading only needed parts.

2. Step 2: Importance of unique keys

   Assigning unique keys to each island prevents hydration conflicts and ensures smooth interactivity.

3. Final Answer:

   Wrap each button in its own <ISLAND> with unique keys to hydrate only needed parts -> Option D

4. Quick Check:

   Separate islands with keys = better performance [OK]

Hint: Use separate islands with unique keys for many interactive parts [OK]

Common Mistakes:

• Grouping all buttons in one island causing unnecessary hydration
• Not using ISLAND tags and hydrating whole page
• Misusing ISLAND on static content