Slots for content projection in Astro

Introduction

Slots let you put custom content inside a component. It helps you reuse components but show different things inside them.

You want a card component that can show different titles and body text each time.

You build a modal component and want to insert any content inside it.

You create a layout component and want to place different page content inside.

You want to make a button component that can have icons or text inside.

You want to wrap content with a styled container but keep the content flexible.

Syntax

Astro

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

<!-- Usage -->
<Component>
  <div slot="slotName">Your content here</div>
</Component>

The <slot> tag marks where content will go inside the component.

Named slots use the name attribute to place specific content.

Examples

This card component has two slots: one for the title and one for the body text.

Astro

--- Card.astro ---
<div class="card">
  <h2><slot name="title"></slot></h2>
  <p><slot name="body"></slot></p>
</div>

Here we fill the card slots with custom title and body content.

Astro

<Card>
  <div slot="title">Hello World</div>
  <div slot="body">This is a simple card.</div>
</Card>

This modal uses a default slot to show any content inside it.

Astro

--- Modal.astro ---
<div class="modal">
  <slot></slot>
</div>

The paragraph will appear inside the modal where the slot is.

Astro

<Modal>
  <p>This is inside the modal!</p>
</Modal>

Sample Program

This example shows a button component with a default slot. You can put any content inside the button when you use it.

Astro

--- Button.astro ---
<button class="btn">
  <slot></slot>
</button>

--- Usage.astro ---
---
import Button from './Button.astro';
---
<Button>Click me!</Button>
<Button><strong>Bold Text</strong></Button>

Important Notes

If you don't provide content for a slot, it will be empty unless you add fallback content inside the slot tag.

Slots help keep components flexible and reusable by letting you change inner content easily.

Summary

Slots let you insert custom content inside components.

Named slots let you place different pieces of content in specific places.

Use slots to make components flexible and reusable.

Practice

1. What is the main purpose of using slots in Astro components?

easy

A. To define styles for a component

B. To handle component state

C. To insert custom content inside a component from outside

D. To fetch data from an API

Solution

1. Step 1: Understand what slots do

   Slots allow you to place custom content inside a component from outside it, making the component flexible.

2. Step 2: Compare with other options

   Styles, state, and data fetching are unrelated to slots' main purpose.

3. Final Answer:

   To insert custom content inside a component from outside -> Option C

4. Quick Check:

   Slots = insert custom content [OK]

Hint: Slots = placeholders for outside content inside components [OK]

Common Mistakes:

• Thinking slots manage styles or state
• Confusing slots with data fetching
• Believing slots are only for static content

2. Which of the following is the correct syntax to define a named slot called header in an Astro component?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall Astro slot syntax

   Named slots use the syntax to define where content goes.

2. Step 2: Check other options

   Other syntaxes like , , or are invalid in Astro.

3. Final Answer:

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

4. Quick Check:

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

Hint: Named slots use syntax [OK]

Common Mistakes:

• Using custom tags like
• Confusing named slots with other frameworks
• Omitting the name attribute

3. Given this Astro component usage:

<MyComponent>
  <h1 slot="title">Welcome</h1>
  <p>Enjoy your stay</p>
</MyComponent>

And inside MyComponent.astro you have:

<slot name="title" />
<slot />

What will be rendered?

medium

A. WelcomeEnjoy your stay

B. Enjoy your stayWelcome

C. Welcome

D. Enjoy your stay

Solution

1. Step 1: Match named slot content

   The <h1> has slot="title", so it fills <slot name="title" /> in the component.

2. Step 2: Match default slot content

   The <p> has no slot attribute, so it fills the default <slot />.

3. Final Answer:

   <h1>Welcome</h1><p>Enjoy your stay</p> -> Option A

4. Quick Check:

   Named slot + default slot = both contents rendered [OK]

Hint: Named slot content fills named slot; others fill default slot [OK]

Common Mistakes:

• Assuming order swaps between slots
• Ignoring slot attribute on elements
• Thinking default slot only renders named slot content

4. What is wrong with this Astro component usage?

<MyComponent>
  <div slot="footer">Footer content</div>
</MyComponent>

And inside MyComponent.astro you have:

<slot name="header" />
<slot />

medium

A. The slot named "footer" is not defined inside the component

B. Slots cannot be used with <div> elements

C. The default slot is missing a name attribute

D. The component must have only one slot

Solution

1. Step 1: Check slot names in component

   The component defines slots named "header" and default (unnamed), but no "footer" slot.

2. Step 2: Check usage slot names

   The usage tries to fill a "footer" slot which does not exist, so content won't render.

3. Final Answer:

   The slot named "footer" is not defined inside the component -> Option A

4. Quick Check:

   Undefined slot name = no content rendered [OK]

Hint: Slot names must match exactly between usage and component [OK]

Common Mistakes:

• Thinking any slot name works without definition
• Believing slot attribute restricts element types
• Assuming default slot needs a name

5. You want to create a reusable Card component with slots for header, body, and footer. Which Astro component code correctly sets up these named slots?

hard

A.

B.

C.

D.

Solution

1. Step 1: Recall correct slot syntax

   Named slots in Astro use self-closing tags like <slot name="name" /> to define placeholders.

2. Step 2: Evaluate options

   <slot name="header" /> <slot name="body" /> <slot name="footer" /> uses correct self-closing syntax for all three slots. <slot-header /> <slot-body /> <slot-footer /> uses invalid custom tags. <slot name="header"> <slot name="body"> <slot name="footer"> nests slots incorrectly. <slot name="header"></slot> <slot name="body"></slot> <slot name="footer"></slot> uses non-self-closing tags which Astro does not support for slots.

3. Final Answer:

   <slot name="header" /> <slot name="body" /> <slot name="footer" /> -> Option B

4. Quick Check:

   Named slots = self-closing <slot name="..." /> [OK]

Hint: Use self-closing for named slots [OK]

Common Mistakes:

• Using custom tags instead of <slot>
• Nesting slots inside each other
• Using non-self-closing slot tags