Slot basics (default slot) in Svelte - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a default slot in Svelte?

A default slot is a placeholder inside a Svelte component where you can insert any child content when you use that component. If no content is provided, the slot remains empty or shows fallback content.

beginner

How do you define a default slot in a Svelte component?

You add the <slot></slot> tag inside your component's markup. This tag marks where the passed child content will appear.

beginner

What happens if you use a component with a default slot but don't pass any content inside it?

The slot will be empty unless you provide fallback content inside the <slot> tag. Fallback content is shown only when no child content is passed.

beginner

Why are slots useful in Svelte components?

Slots let you create flexible components that can wrap or decorate any content you want. This helps reuse layout or style while letting users decide what content to show inside.

beginner

Show a simple example of a Svelte component using a default slot.

Example:<br><pre>&lt;!-- Box.svelte --&gt;
&lt;div class="box"&gt;
  &lt;slot&gt;Default content here&lt;/slot&gt;
&lt;/div&gt;</pre><br>Usage:<br><pre>&lt;Box&gt;Hello!&lt;/Box&gt;</pre><br>This will render a div with class box containing "Hello!".

What tag do you use to create a default slot in a Svelte component?

A <slot></slot>

B <content></content>

C <insert></insert>

D <child></child>

The correct tag for slots in Svelte is .

If no content is passed to a default slot, what will be shown?

A The component does not render

B An error is thrown

C The slot shows the last passed content

D The slot shows fallback content if provided

Slots can have fallback content inside the tag that shows when no content is passed.

Why use slots in Svelte components?

A To allow flexible content inside reusable components

B To style components with CSS

C To fetch data from APIs

D To create animations

Slots let you insert any child content inside a component, making it flexible and reusable.

How do you pass content to a default slot when using a component?

A Use a special attribute

B Use a separate slot component

C Place the content between the component tags

D You cannot pass content to default slots

Content placed between the component's opening and closing tags fills the default slot.

What will this render?

<Box></Box>

Given <slot>Hello</slot> inside Box.svelte?

A An empty box

B A box with the text 'Hello'

C An error

D Nothing renders

Since no content is passed, the fallback 'Hello' inside the slot is shown.

Explain what a default slot is in Svelte and how it works.

Think about how you can insert content inside a reusable box.

Describe a simple example of using a default slot in a Svelte component and how to pass content to it.

Imagine wrapping some text inside a custom box component.

Practice

1. What is the purpose of the default slot in a Svelte component?

easy

A. To display content passed from the parent component if no named slot is used

B. To define a CSS style inside the component

C. To handle component state changes

D. To import external JavaScript files

Solution

1. Step 1: Understand what a slot does

   A slot allows a parent component to pass content into a child component.

2. Step 2: Identify the role of the default slot

   The default slot is the unnamed slot that receives content if no specific slot name is given.

3. Final Answer:

   To display content passed from the parent component if no named slot is used -> Option A

4. Quick Check:

   Default slot = main content placeholder [OK]

Hint: Default slot shows passed content if no slot name given [OK]

Common Mistakes:

• Confusing slots with CSS or state
• Thinking default slot is for styles
• Assuming default slot imports scripts

2. Which of the following is the correct syntax to define a default slot in a Svelte component?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall slot syntax in Svelte

   The default slot is defined simply with <slot></slot> without a name attribute.

2. Step 2: Check the options for correct syntax

   Only uses <slot></slot> without a name, which is correct for the default slot.

3. Final Answer:

   <slot></slot> -> Option A

4. Quick Check:

   Default slot = <slot></slot> [OK]

Hint: Default slot uses <slot> without name attribute [OK]

Common Mistakes:

• Adding name="default" attribute incorrectly
• Using custom tags like
• Confusing named slots with default slot syntax

3. Given the following Svelte component code, what will be rendered?

<!-- Child.svelte -->
<slot>No content provided</slot>

<!-- Parent.svelte -->
<Child>
  <p>Hello from parent</p>
</Child>

medium

A. No content provided

B. Hello from parent

C. An empty space

D. Error: slot not found

Solution

1. Step 1: Understand default slot behavior

   The <slot> tag shows content passed from the parent if any is provided.

2. Step 2: Check if parent passes content

   The parent passes <p>Hello from parent</p> inside <Child>, so this content replaces the default slot fallback.

3. Final Answer:

   Hello from parent -> Option B

4. Quick Check:

   Parent content replaces default slot fallback [OK]

Hint: Parent content overrides default slot fallback text [OK]

Common Mistakes:

• Assuming fallback text always shows
• Thinking slot content is ignored
• Expecting an error when slot is used

4. Identify the error in this Svelte component using a default slot:

<slot name>Fallback</slot>

medium

A. The fallback content must be outside the slot tag

B. Slots cannot have fallback content

C. The slot tag should not have a name attribute without a value

D. The slot tag must be self-closing

Solution

1. Step 1: Analyze the slot tag attributes

   The slot tag has a name attribute but no value, which is invalid syntax.

2. Step 2: Recall correct slot syntax

   Named slots require a name with a string value, or omit the name attribute for default slot.

3. Final Answer:

   The slot tag should not have a name attribute without a value -> Option C

4. Quick Check:

   Empty name attribute on slot is invalid [OK]

Hint: Name attribute must have a value or be omitted [OK]

Common Mistakes:

• Leaving name attribute empty
• Thinking fallback content is invalid
• Using self-closing slot tags incorrectly

5. You want a Svelte component to show a message passed from the parent, but if no message is given, it should show "Welcome!" by default. Which code correctly uses the default slot to achieve this?

hard

A.

B. Welcome!

C. {message || 'Welcome!'}

D. Welcome!

Solution

1. Step 1: Understand default slot fallback usage

   The default slot shows fallback content if no content is passed from the parent.

2. Step 2: Identify correct fallback syntax

   Using <slot>Welcome!</slot> sets "Welcome!" as fallback text correctly.

3. Step 3: Check other options for errors

   <slot name="default">Welcome!</slot> incorrectly uses name="default" which is unnecessary; C uses invalid expression inside slot; D uses non-existent fallback attribute.

4. Final Answer:

   <slot>Welcome!</slot> -> Option D

5. Quick Check:

   Default slot fallback = content inside <slot> [OK]

Hint: Put fallback text inside <slot> tags for default content [OK]

Common Mistakes:

• Adding name="default" attribute unnecessarily
• Trying to use JavaScript expressions inside slot tags
• Using invalid fallback attributes