Rest parameters in Svelte - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to collect all remaining props into a rest object.

Svelte

<script>
  export let name;
  export let age;
  export let [1];
</script>

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

Aprops

Brest

C...rest

D...props

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the three dots (...) before the variable name.

Using a variable name without the spread operator.

In Svelte, using 'export let ...rest;' collects all remaining props into the 'rest' object.

2fill in blank

medium

Complete the code to pass all rest props to the <button> element.

Svelte

<script>
  export let label;
  export let [1];
</script>

<button [1]>{label}</button>

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

A...rest

Brest

Cprops

D...props

Attempts:

3 left

💡 Hint

Common Mistakes

Using rest without the spread operator in the element.

Using a different variable name than the exported rest.

Using {...rest} spreads all rest props onto the button element.

3fill in blank

hard

Fix the error in the rest parameter declaration.

Svelte

<script>
  export let name;
  export let age;
  export let [1];
</script>

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

Arest

Bprops

C...props

D...rest

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the three dots in the rest parameter.

Using a variable name without the spread operator.

Rest parameters must use the spread operator '...' before the variable name.

4fill in blank

hard

Fill both blanks to correctly collect and spread rest props in a Svelte component.

Svelte

<script>
  export let title;
  export let [1];
</script>

<h1>{title}</h1>
<button [2]>Click me</button>

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

A...rest

Brest

C...props

D{...rest}

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for export and spread.

Forgetting the spread operator in either place.

Use 'export let ...rest;' to collect rest props and then spread them with '{...rest}' on the element.

5fill in blank

hard

Fill both blanks to create a Svelte component that collects rest props and passes them to a div with a class.

Svelte

<script>
  export let heading;
  export let [1];
</script>

<div class="container" [2]>
  <h2>{heading}</h2>
  <p>Content here</p>
</div>

<style>
  .container {
    padding: 1rem;
    border: 1px solid #ccc;
  }
</style>

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

A...rest

Brest

C...props

D{...rest}

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for export and spread.

Forgetting the spread operator in export or in the element.

Export rest props with '...rest' and spread them on the div using '{...rest}'. The variable name must match.

Practice

1. In Svelte, what does the rest parameter syntax ...props inside a component's export let statement do?

easy

A. It creates a new event handler for all properties.

B. It limits the component to accept only one property named props.

C. It collects all extra passed properties into an object called props.

D. It automatically binds all properties to the component's state.

Solution

1. Step 1: Understand rest parameters in Svelte

   Rest parameters collect all extra properties passed to a component that are not explicitly declared.

2. Step 2: Analyze the syntax export let ...props

   This syntax gathers all remaining props into an object named props, allowing flexible access.

3. Final Answer:

   It collects all extra passed properties into an object called props. -> Option C

4. Quick Check:

   Rest parameters = collect extra props [OK]

Hint: Rest parameters gather extra inputs into one object [OK]

Common Mistakes:

• Thinking rest parameters limit props instead of collecting them
• Confusing rest parameters with event handlers
• Assuming rest parameters auto-bind to state

2. Which of the following is the correct way to declare a rest parameter to collect extra props in a Svelte component?

easy

A. export let ...restProps;

B. export let restProps = ...;

C. export let ...restProps = {};

D. export let restProps...;

Solution

1. Step 1: Recall correct rest parameter syntax in Svelte

   Rest parameters use the spread operator ... before the variable name in export let.

2. Step 2: Check each option's syntax

   export let ...restProps; correctly uses export let ...restProps;. Options A, C, and D misuse assignment or spread placement.

3. Final Answer:

   export let ...restProps; -> Option A

4. Quick Check:

   Rest parameter syntax = export let ...name; [OK]

Hint: Rest parameters use ... before variable name without assignment [OK]

Common Mistakes:

• Adding assignment (=) with rest parameters
• Placing ... after variable name
• Using invalid syntax like ...restProps = {}

3. Given this Svelte component code:

  <script>
    export let name;
    export let ...restProps;
  </script>

  <h1>Hello {name}!</h1>
  <pre>{JSON.stringify(restProps)}</pre>

And this usage:

<MyComponent name="Anna" age={30} city="NY" />

What will be rendered inside the <pre> tag?

medium

A. {"age":30,"city":"NY"}

B. {"name":"Anna"}

C. {"name":"Anna","age":30,"city":"NY"}

D. SyntaxError

Solution

1. Step 1: Understand restProps collects extra props

   The declared prop name is separate; restProps collects all other props like age and city.

2. Step 2: Check what JSON.stringify(restProps) outputs

   It outputs an object with keys age and city and their values.

3. Final Answer:

   {"age":30,"city":"NY"} -> Option A

4. Quick Check:

   Rest props exclude declared props [OK]

Hint: Rest props exclude declared props, collect the rest [OK]

Common Mistakes:

• Including declared props inside restProps
• Expecting all props in restProps
• Confusing restProps with a syntax error

4. Consider this Svelte component snippet:

<script>
  export let ...props;
  console.log(props);
</script>

When you try to compile this, what error will you get?

medium

A. TypeError: Cannot use rest parameter here

B. No error, props logs correctly

C. ReferenceError: props is not defined

D. SyntaxError: Rest parameter must be last in export list

Solution

1. Step 1: Check rest parameter rules in Svelte

   Rest parameters must be the last in the export list and cannot be declared alone if other exports exist.

2. Step 2: Analyze the code snippet

   The snippet uses only one rest parameter export, which is valid. However, Svelte currently does not support rest parameters alone in export let statements; this causes a syntax error.

3. Final Answer:

   SyntaxError: Rest parameter must be last in export list -> Option D

4. Quick Check:

   Rest parameters have strict placement rules [OK]

Hint: Rest parameters must be last and cannot be alone in export list [OK]

Common Mistakes:

• Thinking rest parameters require other exports first
• Expecting syntax error on valid single rest declaration
• Confusing rules for multiple exports with single case

5. You want to create a Svelte component that accepts any number of extra HTML attributes and applies them to a <button> element. Which code correctly uses rest parameters to achieve this?

hard

A. <script>
export let ...attrs;
</script>

<button {...attrs}>Click me</button>

B. <script>
export let attrs = {};
</script>

<button {...attrs}>Click me</button>

C. <script>
export let ...attrs = {};
</script>

<button {...attrs}>Click me</button>

D. <script>
export let attrs;
</script>

<button {...attrs}>Click me</button>

Solution

1. Step 1: Understand Svelte's handling of extra HTML attributes

   Svelte does not currently support rest parameters in export let to collect arbitrary extra HTML attributes.

2. Step 2: Use a single prop with default empty object

   Declaring export let attrs = {}; and spreading {...attrs} on the button is the correct way to accept and apply extra attributes.

3. Final Answer:

   export let attrs = {}; with <button {...attrs}> -> Option B

4. Quick Check:

   Use a single prop object for extra attributes [OK]

Hint: Use a single prop object and spread it on element [OK]

Common Mistakes:

• Assigning default empty object to rest parameter
• Not using rest parameter syntax for extra props
• Passing undefined attrs without rest parameter