*ngSwitch for multiple conditions in Angular - Mini Project: Build & Apply

Using *ngSwitch for Multiple Conditions in Angular

📖 Scenario: You are building a simple Angular component that shows different messages based on a user's role. The roles can be 'admin', 'editor', or 'viewer'. You want to display a unique message for each role using Angular's *ngSwitch directive.

🎯 Goal: Create an Angular standalone component that uses *ngSwitch to display different messages for the roles 'admin', 'editor', and 'viewer'.

📋 What You'll Learn

Create a variable called userRole with the value 'editor'.

Create a variable called roles that holds the list ['admin', 'editor', 'viewer'].

Use *ngSwitch on userRole to show different messages for each role.

Add a default message for any role not in the list.

💡 Why This Matters

🌍 Real World

Many web apps need to show different content based on user roles or states. Using *ngSwitch helps manage these multiple conditions cleanly in Angular templates.

💼 Career

Understanding *ngSwitch is important for Angular developers to build dynamic user interfaces that respond to different data or user roles.

1

Set up the user role variable

Create a variable called userRole and set it to the string 'editor' inside the Angular component class.

Angular

import { Component } from '@angular/core';

@Component({
  selector: 'app-role-message',
  standalone: true,
  template: ``,
})
export class RoleMessageComponent {
  // Create userRole variable here
}

Hint

Use userRole = 'editor'; inside the class to create the variable.

2

Add the roles list variable

Add a variable called roles that holds the array ['admin', 'editor', 'viewer'] inside the Angular component class, below userRole.

Angular

import { Component } from '@angular/core';

@Component({
  selector: 'app-role-message',
  standalone: true,
  template: ``,
})
export class RoleMessageComponent {
  userRole = 'editor';
  // Add roles array here
}

Hint

Use roles = ['admin', 'editor', 'viewer']; to create the list.

3

Use *ngSwitch to show messages for each role

In the component's template, use a div with *ngSwitch on userRole. Inside it, add *ngSwitchCase blocks for 'admin', 'editor', and 'viewer' that display the messages: 'Welcome Admin!', 'Hello Editor!', and 'Greetings Viewer!' respectively.

Angular

import { Component } from '@angular/core';

@Component({
  selector: 'app-role-message',
  standalone: true,
  template: `
    
    
      
      
      
    
  `,
})
export class RoleMessageComponent {
  userRole = 'editor';
  roles = ['admin', 'editor', 'viewer'];
}

Hint

Use *ngSwitch="userRole" on a container and add *ngSwitchCase="'admin'", *ngSwitchCase="'editor'", and *ngSwitchCase="'viewer'" inside it.

4

Add a default message with *ngSwitchDefault

Add a *ngSwitchDefault block inside the *ngSwitch container that shows the message 'Role not recognized.' for any role not matching the cases.

Angular

import { Component } from '@angular/core';

@Component({
  selector: 'app-role-message',
  standalone: true,
  template: `
    
      Welcome Admin!
      Hello Editor!
      Greetings Viewer!
      
    
  `,
})
export class RoleMessageComponent {
  userRole = 'editor';
  roles = ['admin', 'editor', 'viewer'];
}

Hint

Add <p *ngSwitchDefault>Role not recognized.</p> inside the *ngSwitch container.

Practice

1. What is the main purpose of the Angular directive *ngSwitch?

easy

A. To loop through a list of items and display them

B. To bind data from the component to the template

C. To display one template among many based on a matching value

D. To handle user input events like clicks

Solution

1. Step 1: Understand the role of *ngSwitch

   *ngSwitch is used to conditionally display one of many templates based on a value.

2. Step 2: Compare with other directives

   Unlike loops or event handlers, *ngSwitch chooses one template to show from multiple options.

3. Final Answer:

   To display one template among many based on a matching value -> Option C

4. Quick Check:

   *ngSwitch shows one option based on value = B [OK]

Hint: Remember *ngSwitch picks one view based on a value [OK]

Common Mistakes:

• Confusing *ngSwitch with *ngFor for looping
• Thinking *ngSwitch handles events
• Using *ngSwitch for data binding only

2. Which of the following is the correct syntax to use *ngSwitchCase inside an *ngSwitch block?

easy

A. Content

B. Content

C. Content

D. Content

Solution

1. Step 1: Recall Angular structural directive syntax

   Angular uses *directiveName="expression" syntax for structural directives.

2. Step 2: Match correct syntax for *ngSwitchCase

   The correct syntax is *ngSwitchCase="value", with quotes around the value.

3. Final Answer:

   <div *ngSwitchCase="value">Content</div> -> Option A

4. Quick Check:

   *ngSwitchCase uses = and quotes = A [OK]

Hint: Use *ngSwitchCase="value" with quotes and equals [OK]

Common Mistakes:

• Using colon instead of equals
• Missing the asterisk (*) before ngSwitchCase
• Using wrong attribute name like ngSwitch-case

3. Given this Angular template snippet:

<div [ngSwitch]="color">
  <div *ngSwitchCase="'red'">Stop</div>
  <div *ngSwitchCase="'green'">Go</div>
  <div *ngSwitchCase="'yellow'">Wait</div>
  <div *ngSwitchDefault>Unknown</div>
</div>

What will be displayed if color = 'yellow'?

medium

A. Go

B. Wait

C. Stop

D. Unknown

Solution

1. Step 1: Identify the value of color

   The variable color is set to 'yellow'.

2. Step 2: Match color with *ngSwitchCase values

   The case *ngSwitchCase="'yellow'" matches the value.

3. Final Answer:

   Wait -> Option B

4. Quick Check:

   color='yellow' shows 'Wait' = A [OK]

Hint: Match the variable value exactly with ngSwitchCase string [OK]

Common Mistakes:

• Choosing default when a case matches
• Confusing case strings with variables
• Ignoring quotes around case values

4. What is wrong with this Angular snippet?

<div [ngSwitch]="status">
  <div *ngSwitchCase=active>Active</div>
  <div *ngSwitchCase="inactive">Inactive</div>
  <div *ngSwitchDefault>Unknown</div>
</div>

medium

A. Missing quotes around the first *ngSwitchCase value

B. Using [ngSwitch] instead of *ngSwitch

C. No *ngSwitchDefault provided

D. Using *ngSwitchCase instead of *ngSwitchWhen

Solution

1. Step 1: Check syntax of *ngSwitchCase values

   The first case uses *ngSwitchCase=active without quotes, which is invalid for string values.

2. Step 2: Confirm correct usage of quotes

   String values must be in quotes like *ngSwitchCase="'active'" or *ngSwitchCase="active" if active is a variable.

3. Final Answer:

   Missing quotes around the first *ngSwitchCase value -> Option A

4. Quick Check:

   String case values need quotes = C [OK]

Hint: Always quote string values in *ngSwitchCase [OK]

Common Mistakes:

• Omitting quotes around string cases
• Confusing [ngSwitch] with *ngSwitch
• Forgetting *ngSwitchDefault block

5. You want to display different messages for user roles: 'admin', 'editor', 'guest', and a default for others. Which Angular template correctly uses *ngSwitch to handle this?

hard

A.
Admin Panel
Editor Dashboard
Welcome Guest
Access Denied

B.
Admin Panel
Editor Dashboard
Welcome Guest
Access Denied

C.
Admin Panel
Editor Dashboard
Welcome Guest
Access Denied

D.
Admin Panel
Editor Dashboard
Welcome Guest
Access Denied

Solution

1. Step 1: Check the main [ngSwitch] binding

   The main switch must use property binding syntax: [ngSwitch]="userRole".

2. Step 2: Verify *ngSwitchCase values are strings with quotes

   Each case value is a string and must be quoted like *ngSwitchCase="'admin'".

3. Step 3: Confirm default case is present

   The default case uses *ngSwitchDefault without a value, which is correct.

4. Final Answer:

   Correctly uses [ngSwitch] and quotes string cases -> Option D

5. Quick Check:

   Use [ngSwitch] and quote string cases = D [OK]

Hint: Use [ngSwitch] and quote string cases in *ngSwitchCase [OK]

Common Mistakes:

• Using *ngSwitch instead of [ngSwitch]
• Not quoting string case values
• Missing *ngSwitchDefault block