Why Astro excels at performance - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Astro component correctly.

Astro

import [1] from 'astro';

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

AVue

BComponent

CReact

DAstro

Attempts:

3 left

💡 Hint

Common Mistakes

Using React or Vue imports instead of Astro.

Misspelling the import name.

The correct import is Astro from the 'astro' package to use Astro features.

2fill in blank

medium

Complete the code to define a partial hydration in Astro.

Astro

<MyComponent client:[1] />

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

Aidle

Bload

Conly

Dvisible

Attempts:

3 left

💡 Hint

Common Mistakes

Using client:load which hydrates immediately.

Using client:only which hydrates on page load.

Using client:idle tells Astro to hydrate the component only when the browser is idle, improving performance.

3fill in blank

hard

Fix the error in the Astro component export syntax.

Astro

export default function [1]() { return <div>Hello</div>; }

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

Adefault

BMyComponent

CComponent

DastroComponent

Attempts:

3 left

💡 Hint

Common Mistakes

Using reserved words as function names.

Leaving the function unnamed.

The component must have a valid function name like MyComponent for export default.

4fill in blank

hard

Fill both blanks to create a partial hydration with client:idle and import a component.

Astro

import [1] from './Button.astro';

<[2] client:idle />

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

AButton

BMyButton

CButtonComponent

DBtn

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching import and component names.

Using hydration directives incorrectly.

The imported component and the tag name must match exactly, here both are Button.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that filters components by hydration strategy.

Astro

const hydratedComponents = {
  [1]: component for component in components
  if component.hydration === '[2]' && component.size [3] 100
};

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

Aname

Bidle

C<

Dload

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong keys for the dictionary.

Incorrect comparison operators.

Filtering with wrong hydration values.

This comprehension creates a dictionary with component names where hydration is 'idle' and size is less than 100.

Practice

1. Why does Astro send less code to the browser compared to other frameworks?

easy

A. Because it uses server-side rendering only without any client code

B. Because it compiles code into a single large JavaScript file

C. Because it only sends the HTML and CSS needed, not all JavaScript by default

D. Because it disables CSS to reduce code size

Solution

1. Step 1: Understand Astro's code sending strategy

   Astro sends only the HTML and CSS needed for the page, avoiding unnecessary JavaScript by default.

2. Step 2: Compare with other options

   Other frameworks often send all JavaScript upfront or disable CSS, which is not true for Astro.

3. Final Answer:

   Because it only sends the HTML and CSS needed, not all JavaScript by default -> Option C

4. Quick Check:

   Less code sent = only needed HTML/CSS sent [OK]

Hint: Astro sends minimal code by default, mainly HTML and CSS [OK]

Common Mistakes:

• Thinking Astro sends all JavaScript upfront
• Believing Astro disables CSS to reduce size
• Confusing Astro with frameworks that bundle all code

2. Which of the following is the correct way to load JavaScript only when needed in Astro?

easy

A. ...

B.

C.

D. ...

Solution

1. Step 1: Identify Astro's client directives

   Astro uses client directives like client:load or client:visible to load JavaScript only when needed.

2. Step 2: Match correct syntax

   <MyComponent client:visible>...</MyComponent> is the correct way to load JS when the component becomes visible.

3. Final Answer:

   <MyComponent client:visible>...</MyComponent> -> Option A

4. Quick Check:

   Use client directives to load JS only when needed [OK]

Hint: Look for components with client:visible directive to defer JS [OK]

Common Mistakes:

• Using plain <script> tags without defer or client directives
• Confusing import inside <script> as lazy loading
• Using client:always which loads JS immediately

3. Given this Astro component snippet:

<MyWidget client:idle />

What happens to the JavaScript for MyWidget?

medium

A. It loads only when the browser is idle

B. It loads immediately when the page loads

C. It never loads, only HTML is sent

D. It loads only when the user clicks the widget

Solution

1. Step 1: Understand client:idle directive

   The client:idle directive tells Astro to load the JavaScript when the browser is idle, not immediately.

2. Step 2: Compare other options

   Loading immediately is client:load, never loading is incorrect, and loading on click is client:click.

3. Final Answer:

   It loads only when the browser is idle -> Option A

4. Quick Check:

   client:idle means load JS when browser is idle [OK]

Hint: client:idle defers JS until browser is free [OK]

Common Mistakes:

• Assuming client:idle loads JS immediately
• Confusing client:idle with client:click
• Thinking JS never loads with client:idle

4. You wrote this Astro code:

<MyComponent client:load />

But the JavaScript never loads on the client. What is the likely problem?

medium

A. Astro does not support client-side JavaScript

B. client:load is not a valid directive in Astro

C. You need to add defer attribute to the script tag

D. You forgot to import MyComponent in the Astro file

Solution

1. Step 1: Check if MyComponent is imported

   Astro requires components to be imported before usage; missing import means no JS bundle is generated.

2. Step 2: Validate client:load directive

   client:load is a valid directive, so the issue is not the directive itself.

3. Final Answer:

   You forgot to import MyComponent in the Astro file -> Option D

4. Quick Check:

   Missing import means JS won't load [OK]

Hint: Always import components before using client directives [OK]

Common Mistakes:

• Thinking client:load is invalid
• Assuming Astro disables client JS
• Adding defer attribute manually instead of using directives

5. You want to build a blog with Astro that loads JavaScript only for interactive widgets when visible, and sends static HTML for the rest. Which approach best achieves this?

hard

A. Use <script> tags with defer for all widgets

B. Use <MyWidget client:visible /> for widgets and normal Astro components for static content

C. Disable JavaScript globally and use only server rendering

D. Wrap all components in <AstroIsland client:load> to load JS immediately

Solution

1. Step 1: Identify how to load JS only when widgets are visible

   The client:visible directive loads JavaScript only when the widget scrolls into view, saving resources.

2. Step 2: Use normal Astro components for static content

   Static content can be rendered as plain HTML without JavaScript, improving performance.

3. Final Answer:

   Use <MyWidget client:visible /> for widgets and normal Astro components for static content -> Option B

4. Quick Check:

   client:visible loads JS on visibility, static content stays HTML [OK]

Hint: Use client:visible for widgets, normal components for static parts [OK]

Common Mistakes:

• Loading all JS immediately wastes resources
• Disabling JS globally breaks interactivity
• Using plain <script> tags misses Astro's lazy loading