Named slots in Svelte

Introduction

Named slots let you put different pieces of content into specific places inside a component. This helps you organize and reuse parts easily.

You want to create a card component with separate header, body, and footer areas.

You need to build a modal where the title and buttons come from outside the component.

You want to make a layout component that accepts different content for sidebar and main area.

You want to allow users to customize parts of a component without changing its structure.

Syntax

Svelte

<slot name="slotName"></slot>

Use with a name attribute inside the component to mark where content goes.

When using the component, wrap content in elements with the slot attribute matching the name, e.g.,

.

Examples

Defines three slots: a named header, a default slot, and a named footer.

Svelte

<!-- Inside component -->
<slot name="header"></slot>
<slot></slot> <!-- default slot -->
<slot name="footer"></slot>

Passes content to the named slots and default slot.

Svelte

<!-- Using component -->
<MyComponent>
  <h1 slot="header">Title here</h1>
  <p>Main content goes here.</p>
  <footer slot="footer">Footer text</footer>
</MyComponent>

Sample Program

This example shows a Card component with named slots for header and footer, plus a default slot for the body. The App component fills each slot with custom content.

Svelte

<!-- Card.svelte -->
<div class="card">
  <header class="card-header">
    <slot name="header">Default Header</slot>
  </header>
  <section class="card-body">
    <slot>Default Body Content</slot>
  </section>
  <footer class="card-footer">
    <slot name="footer">Default Footer</slot>
  </footer>
</div>

<!-- App.svelte -->
<script>
  import Card from './Card.svelte';
</script>

<Card>
  <h2 slot="header">Welcome!</h2>
  <p>This is the main card content.</p>
  <small slot="footer">© 2024</small>
</Card>

Important Notes

If you don't provide content for a named slot, the default content inside the slot tag will show.

The default slot is the one without a name attribute and catches content without a slot attribute.

Named slots help keep your components flexible and easy to customize.

Summary

Named slots let you place content in specific parts of a component.

Use the slot attribute on elements when using the component to fill named slots.

They make components more reusable and organized.

Practice

1. What is the main purpose of named slots in Svelte components?

easy

A. To allow placing content into specific parts of a component

B. To define component styles globally

C. To handle component state changes

D. To import external JavaScript files

Solution

1. Step 1: Understand what slots do

   Slots let you insert content inside a component from outside.

2. Step 2: Identify the role of named slots

   Named slots let you put content into specific places inside the component, not just one default spot.

3. Final Answer:

   To allow placing content into specific parts of a component -> Option A

4. Quick Check:

   Named slots = specific content placement [OK]

Hint: Named slots = content in specific component areas [OK]

Common Mistakes:

• Confusing slots with styling or state
• Thinking slots import files
• Assuming slots handle events

2. Which of the following is the correct syntax to define a named slot called header inside a Svelte component?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall slot syntax in Svelte

   Svelte uses the <slot> tag with a name attribute to define named slots.

2. Step 2: Match correct attribute

   The attribute to name a slot is name, not id or custom tags.

3. Final Answer:

   <slot name="header"></slot> -> Option D

4. Quick Check:

   Named slot syntax = <slot name="..."> [OK]

Hint: Named slots use syntax [OK]

Common Mistakes:

• Using id instead of name attribute
• Using custom tags instead of <slot>
• Omitting the name attribute

3. Given this Svelte component usage:

<MyComponent>
  <div slot="title">Welcome</div>
  <div slot="footer">Goodbye</div>
</MyComponent>

And inside MyComponent.svelte you have:

<slot name="title">Default Title</slot>
<slot name="footer">Default Footer</slot>

What will be rendered in the browser?

medium

A. Default Title and Default Footer ignoring the passed content

B. Only Welcome is shown, Goodbye is ignored

C. Welcome and Goodbye in their respective slot positions

D. An error occurs because slots are not used correctly

Solution

1. Step 1: Understand slot filling

   Content with slot="title" fills the named slot "title" in the component.

2. Step 2: Match passed content to slots

   The <div slot="title">Welcome</div> replaces the default title slot content, same for footer.

3. Final Answer:

   Welcome and Goodbye in their respective slot positions -> Option C

4. Quick Check:

   Named slots filled = passed content shown [OK]

Hint: Content with slot="name" replaces default slot content [OK]

Common Mistakes:

• Thinking default slot content always shows
• Assuming only default slot works
• Confusing slot attribute usage

4. What is wrong with this usage of named slots?

<MyComponent>
  <div slot="header">Hello</div>
  <div slot="footer">Bye</div>
  <div slot="header">Again</div>
</MyComponent>

Assuming MyComponent defines named slots header and footer.

medium

A. Slots must be direct children of the component, so this is invalid

B. Multiple elements use the same slot name 'header', causing only the last to render

C. Slot names must be unique and cannot be reused in the same component usage

D. There is no error; all content will render in the header slot

Solution

1. Step 1: Check multiple slot usage

   When multiple elements use the same slot name, only the last one is rendered in that slot.

2. Step 2: Understand slot content replacement

   The first header content is replaced by the second because slots accept one content block per name.

3. Final Answer:

   Multiple elements use the same slot name 'header', causing only the last to render -> Option B

4. Quick Check:

   Duplicate slot names = last content wins [OK]

Hint: Only one content block per named slot is rendered [OK]

Common Mistakes:

• Thinking all duplicates render together
• Believing slot names must be unique globally
• Assuming nested slots behave differently

5. You want to create a Svelte component Card with named slots for header, content, and footer. You also want to provide default content for each slot if none is passed. Which code snippet correctly implements this?

hard

A. Default Header
Default Content
Default Footer

B. Default Header
Default Content
Default Footer

C.

D. Default Header
Default Content
Default Footer

Solution

1. Step 1: Use correct named slot syntax with default content

   Named slots require name attribute and default content inside the slot tags.

2. Step 2: Verify all slots have names and defaults

   Default Header Default Content Default Footer correctly names all slots and provides default text inside each slot tag.

3. Final Answer:

   <slot name="header">Default Header</slot> <slot name="content">Default Content</slot> <slot name="footer">Default Footer</slot> -> Option A

4. Quick Check:

   Named slots with defaults = <slot name="...">default</slot> [OK]

Hint: Named slots need name attribute and default content inside [OK]

Common Mistakes:

• Omitting name attribute
• Using slot attribute without value
• Mixing default slot with named slots incorrectly