Declaring props with export let in Svelte - Mini Project: Build & Apply

Declaring props with export let in Svelte

📖 Scenario: You are building a simple Svelte component that shows a greeting message. The message should come from outside the component, so you need to declare a prop to receive it.

🎯 Goal: Create a Svelte component that declares a prop called greeting using export let and displays it inside a <h1> tag.

📋 What You'll Learn

Declare a prop named greeting using export let

Use the greeting prop inside an <h1> tag

The component should render the greeting text passed as a prop

💡 Why This Matters

🌍 Real World

Props let you create reusable components that can show different data depending on where they are used, like greeting messages, user profiles, or product cards.

💼 Career

Understanding how to declare and use props is essential for building interactive and modular UI components in Svelte, a popular modern frontend framework.

1

Create the Svelte component file

Create a new Svelte component file and add the basic <script> and <h1> tags.

Svelte

  // Your code here

Hint

Start with an empty <script> block and an empty <h1> tag below it.

2

Declare the prop with export let

Inside the <script> tag, declare a prop called greeting using export let greeting;.

Svelte

  // Declare the prop greeting here

Hint

Use export let greeting; to declare the prop inside the <script> block.

3

Use the prop inside the component

Inside the <h1> tag, insert the {greeting} expression to display the prop value.

Svelte

  export let greeting;



  

Hint

Use curly braces {} to insert the greeting variable inside the <h1> tag.

4

Complete the component for use

Ensure the component is ready to receive the greeting prop and display it. The final code should have export let greeting; and use {greeting} inside <h1>.

Svelte

  export let greeting;


{greeting}

Hint

Double-check that the prop is declared and used correctly in the component.

Practice

1. What does export let do inside a Svelte component's <script> block?

easy

A. It creates a local variable that cannot be changed.

B. It imports a module from another file.

C. It declares a prop that can be set from outside the component.

D. It defines a function inside the component.

Solution

1. Step 1: Understand the role of export let

   In Svelte, export let declares a property (prop) that the parent component can pass in.

2. Step 2: Differentiate from other uses

   Unlike local variables or imports, export let specifically exposes variables as props for customization.

3. Final Answer:

   It declares a prop that can be set from outside the component. -> Option C

4. Quick Check:

   Props = export let [OK]

Hint: Remember: export let means external prop [OK]

Common Mistakes:

• Confusing export let with import statements
• Thinking export let creates constants
• Assuming export let defines functions

2. Which of the following is the correct syntax to declare a prop named title with a default value of "Hello" in Svelte?

easy

A. export let title = "Hello";

B. let export title = "Hello";

C. export const title = "Hello";

D. let title = export "Hello";

Solution

1. Step 1: Recall correct syntax for props

   In Svelte, props are declared with export let followed by the variable name and optional default value.

2. Step 2: Check each option

   export let title = "Hello"; matches the correct syntax: export let title = "Hello";. Others have wrong order or keywords.

3. Final Answer:

   export let title = "Hello"; -> Option A

4. Quick Check:

   export let + name + = default [OK]

Hint: Use 'export let' before variable name for props [OK]

Common Mistakes:

• Swapping 'let' and 'export' keywords
• Using 'const' instead of 'let' for props
• Placing export after variable name

3. Given this Svelte component code:

<script>
  export let count = 5;
</script>

<p>Count is {count}</p>

What will be displayed if the component is used as <MyComponent count={10} />?

medium

A. Count is 5

B. Count is 10

C. Count is undefined

D. Syntax error

Solution

1. Step 1: Understand default and passed props

   The component sets a default count of 5, but the parent passes 10, which overrides the default.

2. Step 2: Determine rendered output

   The displayed text uses the passed value 10, so it shows "Count is 10".

3. Final Answer:

   Count is 10 -> Option B

4. Quick Check:

   Passed prop overrides default [OK]

Hint: Passed props override defaults [OK]

Common Mistakes:

• Assuming default always shows ignoring passed value
• Thinking undefined appears if prop is passed
• Confusing syntax error with valid code

4. Identify the error in this Svelte component code:

<script>
  export let name;
  name = "John";
</script>

<p>Hello {name}</p>

medium

A. You cannot assign a value to a prop inside the component after declaration.

B. Missing default value for the prop name.

C. The export keyword should be after let.

D. The <p> tag cannot use curly braces.

Solution

1. Step 1: Understand prop assignment rules

   Props declared with export let should not be reassigned inside the component; they come from outside.

2. Step 2: Check the code

   The code tries to assign name = "John" after declaration, which is not allowed and causes an error.

3. Final Answer:

   You cannot assign a value to a prop inside the component after declaration. -> Option A

4. Quick Check:

   Props are read-only inside component [OK]

Hint: Don't reassign props inside component [OK]

Common Mistakes:

• Trying to set default by assignment after export let
• Confusing export let order
• Misunderstanding template syntax

5. You want to create a Svelte component that accepts a prop items which is an array, but if no prop is passed, it should default to an empty array. Which code correctly declares this prop?

hard

A. export const items = [];

B. export let items;if (!items) items = [];

C. let items = [];

D. export let items = [];

Solution

1. Step 1: Set default value in prop declaration

   In Svelte, you can assign a default value directly when declaring a prop with export let.

2. Step 2: Evaluate options

   export let items = []; correctly declares items with default empty array. export let items;
if (!items) items = []; tries to assign after declaration, which is not allowed. let items = []; is local variable, not prop. export const items = []; uses const which is incorrect for props.

3. Final Answer:

   export let items = []; -> Option D

4. Quick Check:

   Default values go in export let declaration [OK]

Hint: Assign default value in export let line [OK]

Common Mistakes:

• Assigning default after declaration
• Using const instead of let for props
• Not exporting the variable