Access modifiers in components in Angular - Mini Project: Build & Apply

Access modifiers in components

📖 Scenario: You are building a simple Angular component to display user information. You want to control which properties and methods can be accessed from outside the component and which should stay private inside it.

🎯 Goal: Create an Angular standalone component named UserInfoComponent that uses public and private access modifiers correctly to manage its properties and methods.

📋 What You'll Learn

Create a standalone Angular component named UserInfoComponent.

Add a public property called userName with the value 'Alice'.

Add a private property called userAge with the value 30.

Add a public method called getUserAge that returns the value of userAge.

Use the userName property in the component template to display the user's name.

Do not display userAge directly in the template.

💡 Why This Matters

🌍 Real World

In real Angular apps, access modifiers help developers protect sensitive data and control what parts of a component are exposed to templates or other components.

💼 Career

Understanding access modifiers is essential for writing clean, maintainable Angular code and collaborating in teams where component encapsulation matters.

1

Create the component with public userName

Create a standalone Angular component named UserInfoComponent. Inside the component class, add a public property called userName and set it to 'Alice'.

Angular

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

@Component({
  selector: 'app-user-info',
  standalone: true,
  template: `User: {{ userName }}`
})
export class UserInfoComponent {
  // Your code here
}

Hint

Use public userName = 'Alice'; inside the component class.

2

Add a private userAge property

Inside the UserInfoComponent class, add a private property called userAge and set it to 30.

Angular

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

@Component({
  selector: 'app-user-info',
  standalone: true,
  template: `User: {{ userName }}`
})
export class UserInfoComponent {
  public userName = 'Alice';
  // Your code here
}

Hint

Use private userAge = 30; inside the component class.

3

Add a public method to get userAge

Inside the UserInfoComponent class, add a public method called getUserAge that returns the value of the private userAge property.

Angular

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

@Component({
  selector: 'app-user-info',
  standalone: true,
  template: `User: {{ userName }}`
})
export class UserInfoComponent {
  public userName = 'Alice';
  private userAge = 30;
  // Your code here
}

Hint

Define public getUserAge(): number { return this.userAge; } inside the component class.

4

Complete the component template

Ensure the component template uses the userName property to display the user's name inside a paragraph tag. Do not display userAge directly in the template.

Angular

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

@Component({
  selector: 'app-user-info',
  standalone: true,
  template: `User: {{ userName }}`
})
export class UserInfoComponent {
  public userName = 'Alice';
  private userAge = 30;

  public getUserAge(): number {
    return this.userAge;
  }
  // Your code here
}

Hint

The template should only show {{ userName }} inside a paragraph tag.

Practice

1. Which access modifier allows a component property to be used directly in its template in Angular?

easy

A. readonly

B. private

C. protected

D. public

Solution

1. Step 1: Understand template access rules

   Angular templates can only access properties and methods marked as public.

2. Step 2: Compare access modifiers

   private and protected members are not accessible in templates, only public members are.

3. Final Answer:

   public -> Option D

4. Quick Check:

   Templates access public members only [OK]

Hint: Templates can only see public members [OK]

Common Mistakes:

• Thinking private members are accessible in templates
• Confusing protected with public for template access
• Assuming readonly affects visibility

2. Which of the following is the correct syntax to declare a private property named count in an Angular component?

easy

A. count private: number;

B. private count: number;

C. protected count = number;

D. public count: number;

Solution

1. Step 1: Recall TypeScript property declaration syntax

   Access modifier comes first, then property name, colon, and type.

2. Step 2: Check each option

   private count: number; matches correct syntax: private count: number;. public count: number; is public, not private. protected count = number; has wrong assignment syntax. count private: number; has wrong order.

3. Final Answer:

   private count: number; -> Option B

4. Quick Check:

   Access modifier + name + colon + type [OK]

Hint: Access modifier comes before property name [OK]

Common Mistakes:

• Placing access modifier after property name
• Using assignment instead of type annotation
• Mixing up protected and private keywords

3. Consider this Angular component snippet:

export class MyComponent {
  private secret = 'hidden';
  public visible = 'shown';
}

Which property can be accessed in the component's template?

medium

A. secret

B. Both secret and visible

C. visible

D. Neither secret nor visible

Solution

1. Step 1: Identify access modifiers of properties

   secret is private, visible is public.

2. Step 2: Recall template access rules

   Templates can only access public members, so only visible is accessible.

3. Final Answer:

   visible -> Option C

4. Quick Check:

   Only public properties are template-accessible [OK]

Hint: Only public properties show in templates [OK]

Common Mistakes:

• Assuming private properties are accessible in templates
• Thinking both properties are accessible
• Confusing private with protected

4. Identify the error in this Angular component code:

export class DemoComponent {
  private title = 'Hello';
}

// In template:
// <h1>{{ title }}</h1>

medium

A. Template cannot access private property 'title'

B. No error, code works fine

C. Missing semicolon after title declaration

D. title should be declared as protected

Solution

1. Step 1: Check property access modifier

   title is declared private, so it is hidden from outside the class.

2. Step 2: Understand template access rules

   Angular templates can only access public properties, so trying to use title in template causes an error.

3. Final Answer:

   Template cannot access private property 'title' -> Option A

4. Quick Check:

   Private properties are not accessible in templates [OK]

Hint: Templates only see public, not private properties [OK]

Common Mistakes:

• Ignoring access modifier effect on templates
• Thinking missing semicolon causes error
• Confusing protected with private for template access

5. You want a property data in a base Angular component to be accessible in its child components but not directly in the template. Which access modifier should you use?

hard

A. protected

B. private

C. public

D. readonly

Solution

1. Step 1: Understand access modifier meanings

   private hides from all except the class itself, public exposes everywhere including templates, protected allows access in the class and its subclasses but not templates.

2. Step 2: Match requirement to modifier

   Since data should be accessible in child components but hidden from templates, protected fits perfectly.

3. Final Answer:

   protected -> Option A

4. Quick Check:

   Protected = accessible in children, hidden from templates [OK]

Hint: Use protected for child access, hide from templates [OK]

Common Mistakes:

• Choosing public and exposing property to templates
• Using private and blocking child access
• Confusing readonly with access control