Component composition in Svelte - Mini Project: Build & Apply

Component composition

📖 Scenario: You are building a simple Svelte app that shows a list of fruits with their colors. You want to split the UI into smaller parts for better organization.

🎯 Goal: Create two Svelte components: FruitItem.svelte to show one fruit and its color, and FruitList.svelte to show the list of fruits using FruitItem. Compose them so the app displays all fruits with their colors.

📋 What You'll Learn

Create a FruitItem.svelte component that accepts name and color as props and displays them.

Create a FruitList.svelte component that has a list of fruits as an array of objects with name and color.

Use FruitItem inside FruitList to render each fruit.

Ensure the main app file App.svelte renders FruitList.

💡 Why This Matters

🌍 Real World

Component composition is how you build complex user interfaces by combining small, reusable parts. This makes your code easier to manage and update.

💼 Career

Understanding component composition is essential for working with modern frontend frameworks like Svelte, React, or Vue. It is a core skill for frontend developers.

1

Create the FruitItem.svelte component

Create a Svelte component file named FruitItem.svelte. Inside it, declare two props: name and color. Then add markup that shows the fruit name inside a <strong> tag and the color inside a <em> tag.

Svelte

  // Declare props name and color here


{name} is {color}

Hint

Use export let to declare props in Svelte.

2

Create the FruitList.svelte component with fruit data

Create a Svelte component file named FruitList.svelte. Inside it, create a variable called fruits that is an array of objects. Each object should have name and color properties with these exact entries: { name: 'Apple', color: 'red' }, { name: 'Banana', color: 'yellow' }, and { name: 'Grape', color: 'purple' }.

Svelte

  // Create fruits array here

Hint

Use const fruits = [...] to create the array.

3

Use FruitItem inside FruitList.svelte to render each fruit

In FruitList.svelte, import the FruitItem component. Then use a {#each} block to loop over the fruits array. For each fruit, render <FruitItem /> passing name and color as props from the fruit object.

Svelte

  const fruits = [
    { name: 'Apple', color: 'red' },
    { name: 'Banana', color: 'yellow' },
    { name: 'Grape', color: 'purple' }
  ];
  // Import FruitItem here


{#each fruits as fruit}
  
{/each}

Hint

Use import FruitItem from './FruitItem.svelte' and a {#each} block.

4

Render FruitList inside App.svelte

In the main app file App.svelte, import the FruitList component. Then add <FruitList /> inside the markup to show the fruit list on the page.

Svelte

  // Import FruitList here

Hint

Use import FruitList from './FruitList.svelte' and add <FruitList /> in markup.

Practice

1. What is the main purpose of component composition in Svelte?

easy

A. To write all UI code in one big file

B. To build UI by combining smaller components

C. To avoid using any components

D. To make components run faster

Solution

1. Step 1: Understand component composition

   Component composition means creating a UI by putting smaller components together.

2. Step 2: Compare options

   Only To build UI by combining smaller components correctly describes this purpose. Other options are incorrect or unrelated.

3. Final Answer:

   To build UI by combining smaller components -> Option B

4. Quick Check:

   Component composition = combining components [OK]

Hint: Think: How do you build complex UI simply? [OK]

Common Mistakes:

• Thinking composition means one big file
• Believing components slow down the app
• Ignoring the reuse benefit

2. Which of the following is the correct way to include a child component Child.svelte inside Parent.svelte?

easy

A. <script>import Child from './Child.svelte';</script><Child />

B. <Child /> without import

C. <script>import Child from './Child.svelte';</script><child />

D. <script>import './Child.svelte';</script><Child />

Solution

1. Step 1: Check import syntax

   In Svelte, you must import the component with a name, e.g., import Child from './Child.svelte'.

2. Step 2: Use the imported component tag

   Use <Child /> with capital C matching import name. <script>import Child from './Child.svelte';</script><Child /> matches this exactly.

3. Final Answer:

   <script>import Child from './Child.svelte';</script><Child /> -> Option A

4. Quick Check:

   Import + matching tag = correct syntax [OK]

Hint: Always import before using component tags [OK]

Common Mistakes:

• Using component tags without import
• Using lowercase tag names for imported components
• Importing without naming the component

3. Given these two components, what will be rendered inside App.svelte?

// Child.svelte
<h2>Hello from Child</h2>

// App.svelte
<script>
  import Child from './Child.svelte';
</script>

<main>
  <h1>Welcome</h1>
  <Child />
</main>

medium

A. Hello from Child

B. Welcome

C. WelcomeHello from Child

D. Nothing renders due to error

Solution

1. Step 1: Analyze App.svelte structure

   App renders a main with <h1>Welcome</h1> and includes <Child /> component.

2. Step 2: Check Child.svelte output

   Child renders <h2>Hello from Child</h2>.

3. Step 3: Combine outputs

   App will show <h1>Welcome</h1> followed by Child's <h2>Hello from Child</h2>.

4. Final Answer:

   <h1>Welcome</h1><h2>Hello from Child</h2> -> Option C

5. Quick Check:

   Parent + child render combined [OK]

Hint: Child component content appears where tag is placed [OK]

Common Mistakes:

• Ignoring child component output
• Thinking child replaces parent content
• Assuming syntax error without cause

4. What is wrong with this Svelte component composition code?

// Parent.svelte
<script>
  import Child from './Child.svelte';
</script>

<main>
  <child />
</main>

medium

A. Component tag <child /> should be capitalized as <Child />

B. Missing import statement for Child

C. Parent component cannot use Child component

D. The <main> tag is invalid here

Solution

1. Step 1: Check import and usage

   Child is imported as Child with capital C.

2. Step 2: Check component tag case

   Svelte requires component tags to match import name case exactly. <child /> is lowercase and invalid.

3. Final Answer:

   Component tag <child /> should be capitalized as <Child /> -> Option A

4. Quick Check:

   Component tags are case-sensitive [OK]

Hint: Match component tag case to import name exactly [OK]

Common Mistakes:

• Using lowercase component tags
• Forgetting case sensitivity
• Assuming missing import

5. You want to create a Dashboard.svelte that shows a Header, a Sidebar, and a Content component. Which approach correctly composes these components to keep the layout organized and reusable?

hard

A. <script>import Header from './Header.svelte'; import Sidebar from './Sidebar.svelte'; import Content from './Content.svelte';</script>
<Header />
<Sidebar />

B. <script>import Header from './Header.svelte';</script>
<Header />
<Sidebar />
<Content />

C. <script>import * from './components';</script>
<Header /><Sidebar /><Content />

D. <script>import Header from './Header.svelte'; import Sidebar from './Sidebar.svelte'; import Content from './Content.svelte';</script>
<div class='dashboard'>
<Header />
<Sidebar />
<Content />
</div>

Solution

1. Step 1: Check imports for all components

   <script>import Header from './Header.svelte'; import Sidebar from './Sidebar.svelte'; import Content from './Content.svelte';</script> <div class='dashboard'> <Header /> <Sidebar /> <Content /> </div> imports Header, Sidebar, and Content correctly.

2. Step 2: Check usage inside a container

   <script>import Header from './Header.svelte'; import Sidebar from './Sidebar.svelte'; import Content from './Content.svelte';</script> <div class='dashboard'> <Header /> <Sidebar /> <Content /> </div> uses a container div to organize components, making layout clear and reusable.

3. Step 3: Compare other options

   <script>import Header from './Header.svelte';</script> <Header /> <Sidebar /> <Content /> misses imports for Sidebar and Content. <script>import * from './components';</script> <Header /><Sidebar /><Content /> uses invalid import syntax. <script>import Header from './Header.svelte'; import Sidebar from './Sidebar.svelte'; import Content from './Content.svelte';</script> <Header /> <Sidebar /> misses Content usage.

4. Final Answer:

   <script>import Header from './Header.svelte'; import Sidebar from './Sidebar.svelte'; import Content from './Content.svelte';</script> <div class='dashboard'> <Header /> <Sidebar /> <Content /> </div> -> Option D

5. Quick Check:

   Import all + use all components inside container [OK]

Hint: Import and use all components inside one container [OK]

Common Mistakes:

• Forgetting to import all components
• Using invalid import syntax
• Not including all components in layout