ng-content for slot-based composition in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert default content using .

Angular

<div>
  <ng-content [1]></ng-content>
</div>

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

Aselect="header"

Bselect

Cdefault

Dslot

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a select attribute when default content is needed

Using 'slot' attribute which is not valid in Angular

The tag without a select attribute acts as the default slot for content projection.

2fill in blank

medium

Complete the code to project content into a named slot called 'header'.

Angular

<ng-content [1]></ng-content>

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

Aslot="header"

Bid="header"

Cname="header"

Dselect="header"

Attempts:

3 left

💡 Hint

Common Mistakes

Using slot attribute which is not recognized by Angular

Using name or id attributes which do not work for content projection

Use the select attribute with the CSS selector to project content into the named slot 'header'.

3fill in blank

hard

Fix the error in the content projection selector to match elements with attribute 'footer'.

Angular

<ng-content [1]></ng-content>

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

Aselect="footer"

Bselect="[footer]"

Cselect=".footer"

Dselect="#footer"

Attempts:

3 left

💡 Hint

Common Mistakes

Using select="footer" which selects elements named footer, not attributes

Using class or id selectors which do not match attribute selectors

To select elements with an attribute 'footer', use the attribute selector syntax [footer].

4fill in blank

hard

Complete the code to project content with attribute 'sidebar' and default content fallback.

Angular

<ng-content [1]></ng-content>
<ng-content ></ng-content>

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

Aselect="[sidebar]"

Bselect="default"

Dselect="*"

Attempts:

3 left

💡 Hint

Common Mistakes

Using select="default" which is not a valid selector

Adding select attribute to default content projection

The first projects content with attribute 'sidebar'. The second without select projects default content.

5fill in blank

hard

Fill both blanks to project content for 'header', 'footer', and default slots.

Angular

<ng-content [1]></ng-content>
<ng-content [2]></ng-content>
<ng-content ></ng-content>

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

Aselect="header"

Bselect="footer"

Dselect="main"

Attempts:

3 left

💡 Hint

Common Mistakes

Using select attribute for default slot

Mixing up slot names or selectors

Use select="header" and select="footer" for named slots, and no select for default slot.

Practice

1. What is the main purpose of ng-content in Angular components?

easy

A. To define component styles

B. To insert external content inside a component's template

C. To handle component events

D. To create services for dependency injection

Solution

1. Step 1: Understand ng-content role

   ng-content is used to project or insert external HTML content into a component's template.

2. Step 2: Differentiate from other features

   It does not define styles, handle events, or create services; those are unrelated to content projection.

3. Final Answer:

   To insert external content inside a component's template -> Option B

4. Quick Check:

   Content projection = Insert external content [OK]

Hint: Remember: ng-content projects external HTML inside components [OK]

Common Mistakes:

• Confusing ng-content with event handling
• Thinking ng-content styles components
• Mixing ng-content with service creation

2. Which syntax correctly creates a named slot using ng-content in Angular?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recall correct attribute for named slots

   Angular uses the select attribute on ng-content to create named slots by CSS selectors.

2. Step 2: Check each option

   Only uses select with a CSS class selector, which is correct syntax.

3. Final Answer:

   <ng-content select=".header"></ng-content> -> Option A

4. Quick Check:

   Named slot uses select attribute [OK]

Hint: Use select="CSS-selector" for named ng-content slots [OK]

Common Mistakes:

• Using name or slot attributes which Angular does not support
• Confusing with Web Components slot attribute
• Using id attribute instead of select

3. Given this component template:

<div>
  <ng-content select=".title"></ng-content>
  <ng-content select=".body"></ng-content>
</div>

And usage:

<my-comp>
  <h1 class="title">Hello</h1>
  <p class="body">Welcome!</p>
</my-comp>

What will be rendered inside <my-comp>?

medium

A.

B. Welcome!Hello

C. HelloWelcome!

D. HelloWelcome!

Solution

1. Step 1: Match content with selectors

   The ng-content select=".title" inserts elements with class title, and select=".body" inserts elements with class body.

2. Step 2: Check order of insertion

   The template places .title content first, then .body content, so the output matches that order.

3. Final Answer:

   <div><h1 class="title">Hello</h1><p class="body">Welcome!</p></div> -> Option D

4. Quick Check:

   Content order follows ng-content slots [OK]

Hint: Content projects in order of ng-content slots matching selectors [OK]

Common Mistakes:

• Assuming order depends on usage, not template
• Ignoring CSS class selectors in select
• Expecting content without classes to appear

4. What is wrong with this component template?

<div>
  <ng-content select="header"></ng-content>
  <ng-content select=".body"></ng-content>
</div>

Usage:

<my-comp>
  <div class="header">Top</div>
  <div class="body">Content</div>
</my-comp>

medium

A. The usage classes do not match the template selectors

B. The select attribute cannot use class selectors

C. The selector 'header' misses the dot for class, so no content projects there

D. ng-content must have a closing tag with content inside

Solution

1. Step 1: Analyze the select attribute usage

   The first ng-content uses select="header", which looks for elements named <header>, not class header.

2. Step 2: Compare with usage classes

   The usage provides <div class="header">, which does not match the selector header (element selector). It should be .header to match the class.

3. Final Answer:

   The selector 'header' misses the dot for class, so no content projects there -> Option C

4. Quick Check:

   Class selectors need dot prefix in select [OK]

Hint: Class selectors in select need a dot prefix (e.g., .header) [OK]

Common Mistakes:

• Using element name instead of class selector
• Thinking select cannot use class selectors
• Forgetting ng-content can be self-closing

5. You want to create a reusable card component with three slots: header, content, and footer. Which template correctly uses ng-content to support this slot-based composition?

hard

A.

B.

C.

D.

Solution

1. Step 1: Identify correct attribute for named slots

   Angular uses select with CSS selectors to define named slots in ng-content.

2. Step 2: Check each option's syntax

   uses select with class selectors, matching Angular's pattern. Options B, C, and D use invalid selectors or attributes (name, slot) not supported by Angular.

3. Step 3: Confirm semantic HTML usage

   wraps slots in semantic elements (header, section, footer), improving accessibility and structure.

4. Final Answer:

   Option A's template correctly uses ng-content with select and semantic tags -> Option A

5. Quick Check:

   Use select with CSS classes for slots + semantic tags [OK]

Hint: Use select='.class' for slots and wrap with semantic tags [OK]

Common Mistakes:

• Using name or slot attributes instead of select
• Not using CSS selectors in select
• Ignoring semantic HTML for accessibility