Component selector usage in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use the component selector in the template.

Angular

<[1]></[1]>

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

Aapp-hello

Bhello-app

Cmy-component

Dcomponent-app

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong selector name that does not match the component.

Forgetting to close the tag properly.

The component selector is used as a custom HTML tag. Here, app-hello is the correct selector.

2fill in blank

medium

Complete the code to import the component and add it to the template.

Angular

import { HelloComponent } from './hello.component';

@Component({
  selector: 'app-root',
  template: '<[1]></[1]>'
})
export class AppComponent {}

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

Aroot-app

Bhello-app

Capp-hello

Dmain-hello

Attempts:

3 left

💡 Hint

Common Mistakes

Using a selector that does not match the imported component.

Not importing the component before using its selector.

The app-hello selector matches the HelloComponent's selector and is used in the template.

3fill in blank

hard

Fix the error in the component usage by completing the selector tag correctly.

Angular

<div>
  <[1]></[1]>
</div>

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

AhelloApp

BAppHello

CappHello

Dapp-hello

Attempts:

3 left

💡 Hint

Common Mistakes

Using camelCase or PascalCase instead of kebab-case for selectors.

Mismatching opening and closing tags.

Angular component selectors are case-sensitive and use kebab-case. app-hello is correct.

4fill in blank

hard

Fill both blanks to correctly use the component selector with an input property binding.

Angular

<[1] [title]=[2]></[1]>

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

Aapp-hello

B'Welcome'

C"Welcome"

Dhello-app

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes without quotes inside the binding.

Using the wrong selector name.

The selector app-hello is used as the tag, and the input property title is bound to the string "Welcome" using quotes.

5fill in blank

hard

Fill all three blanks to use the component selector with input and output bindings.

Angular

<[1] [user]="[2]" (notify)="[3]"></[1]>

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

Aapp-hello

BcurrentUser

ConNotify()

Dhello-app

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up input and output binding syntax.

Using incorrect selector names.

Forgetting parentheses for event bindings.

The component selector app-hello is used. The input property user is bound to currentUser, and the output event notify is bound to the method onNotify().

Practice

1. What does the selector property in an Angular component define?

easy

A. The HTML tag or attribute used to place the component in templates

B. The CSS styles applied to the component

C. The TypeScript class name of the component

D. The module where the component is declared

Solution

1. Step 1: Understand the role of selector in Angular components

   The selector tells Angular what HTML tag or attribute to look for to insert the component's template.

2. Step 2: Differentiate selector from other properties

   CSS styles and class names are unrelated to selector; selector is specifically for placement in HTML.

3. Final Answer:

   The HTML tag or attribute used to place the component in templates -> Option A

4. Quick Check:

   Selector = HTML tag/attribute [OK]

Hint: Selector defines how to use the component in HTML [OK]

Common Mistakes:

• Confusing selector with styles or class names
• Thinking selector is the component's class name
• Assuming selector defines module info

2. Which of the following is a valid selector syntax for an Angular component?

easy

A. [my-component]

B. my-component

C. .my-component

D. myComponent

Solution

1. Step 1: Recognize selector types in Angular

   Angular selectors can be tag names (like 'my-component'), attribute selectors ('[my-component]'), or class selectors ('.my-component').

2. Step 2: Identify valid selector syntax

   The option 'my-component' is a valid tag selector string used in the selector property. The other options represent attribute or class selectors.

3. Final Answer:

   my-component -> Option B

4. Quick Check:

   Tag selector syntax = tag name string [OK]

Hint: Tag selectors are simple tag names without brackets or dots [OK]

Common Mistakes:

• Using selector syntax directly instead of HTML usage
• Confusing attribute selector brackets with HTML tags
• Using camelCase instead of kebab-case for tags

3. Given this component selector: selector: '[appHighlight]', how would you use it in HTML?

medium

A.

B.

C.

D.

Solution

1. Step 1: Understand attribute selector syntax

   The selector '[appHighlight]' means the component is used as an attribute on an HTML element.

2. Step 2: Match usage to selector

   Using
   applies the component to the div element as an attribute, matching the selector.

3. Final Answer:

   <div appHighlight></div> -> Option C

4. Quick Check:

   Attribute selector = element with attribute [OK]

Hint: Attribute selectors used as attributes on elements [OK]

Common Mistakes:

• Using tag syntax for attribute selectors
• Using class or id instead of attribute
• Forgetting brackets mean attribute selector

4. Why does this Angular component not render?

@Component({ selector: 'my-widget', template: '
Hi
' }) export class MyWidgetComponent {}

Used in HTML as: <my-widget></my-widget>

medium

A. Component is missing @NgModule declarations

B. Selector must be prefixed with 'app-' by Angular rules

C. Selector is correct; problem is elsewhere

D. Selector should be in square brackets for attribute usage

Solution

1. Step 1: Check selector syntax

   The selector 'my-widget' is valid as a tag selector and matches usage <my-widget></my-widget>.

2. Step 2: Verify component registration

   Angular requires components to be declared in an NgModule or standalone to render. Missing declaration causes no rendering.

3. Final Answer:

   Component is missing @NgModule declarations -> Option A

4. Quick Check:

   Missing declaration = no render [OK]

Hint: Component must be declared or standalone to render [OK]

Common Mistakes:

• Thinking selector must have 'app-' prefix
• Confusing attribute selector syntax with tag selector
• Ignoring module declarations

5. You want to create a component that can be used as a CSS class selector. Which selector should you use and how do you apply it in HTML?

hard

A. Use selector: '#fancy-button' and apply as <button id="fancy-button">

B. Use selector: 'fancy-button' and apply as <fancy-button>

C. Use selector: '[fancy-button]' and apply as <button fancy-button>

D. Use selector: '.fancy-button' and apply as <button class="fancy-button">

Solution

1. Step 1: Understand class selector syntax

   To use a component as a CSS class selector, prefix the selector with a dot (.) like '.fancy-button'.

2. Step 2: Apply component in HTML

   Use the component by adding the class attribute with the selector name: <button class="fancy-button">.

3. Final Answer:

   Use selector '.fancy-button' and apply as <button class="fancy-button"> -> Option D

4. Quick Check:

   Class selector = dot prefix + class attribute [OK]

Hint: Class selectors start with dot and used as class attribute [OK]

Common Mistakes:

• Using id selector (#) instead of class selector (.)
• Confusing attribute selector brackets with class selector
• Applying class selector as tag or attribute