Enums in Angular applications - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple enum named Color with values Red, Green, and Blue.

Angular

export enum Color {
  Red = 0,
  Green = 1,
  [1] = 2
}

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

ABlue

BYellow

COrange

DPurple

Attempts:

3 left

💡 Hint

Common Mistakes

Using a color name not declared in the enum.

Skipping the enum member name and only writing the number.

The enum Color includes Blue as the third value with the numeric value 2.

2fill in blank

medium

Complete the code to use the enum Color and assign the value Green to the variable selectedColor.

Angular

import { Color } from './color.enum';

const selectedColor: Color = [1];

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

AColor.Green

BColor.Blue

CColor.Red

DColor.Yellow

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning a string instead of an enum member.

Using a member not declared in the enum.

The variable selectedColor is assigned the enum value Color.Green.

3fill in blank

hard

Fix the error in the enum declaration by completing the missing enum member name.

Angular

export enum Direction {
  Up = 1,
  Down = 2,
  [1] = 3,
  Left = 4
}

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

ABack

BForward

CSide

DRight

Attempts:

3 left

💡 Hint

Common Mistakes

Using a direction name not matching the enum pattern.

Leaving the member name blank or using a number only.

The enum Direction includes Right as the member with value 3.

4fill in blank

hard

Fill both blanks to create an enum Status with string values Active and Inactive.

Angular

export enum Status {
  Active = '[1]',
  Inactive = '[2]'
}

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

Aactive

Binactive

Cenabled

Ddisabled

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase strings instead of lowercase.

Mixing unrelated strings like 'enabled' or 'disabled'.

The enum Status uses string values 'active' and 'inactive' for its members.

5fill in blank

hard

Fill all three blanks to create a function getStatusMessage that returns a message based on the Status enum value.

Angular

import { Status } from './status.enum';

function getStatusMessage(status: Status): string {
  switch (status) {
    case Status.[1]:
      return '[2]';
    case Status.[3]:
      return 'User is inactive';
    default:
      return 'Unknown status';
  }
}

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

AActive

BUser is active

CInactive

DUser is enabled

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong enum member names in the switch cases.

Returning messages that do not match the status.

The function checks if the status is Status.Active and returns 'User is active'. For Status.Inactive, it returns 'User is inactive'.

Practice

1. What is the main purpose of using enum in an Angular application?

easy

A. To group related constant values under a single name

B. To create dynamic variables that change at runtime

C. To define functions inside components

D. To style components with CSS

Solution

1. Step 1: Understand what enums represent

   Enums are used to group related constant values, making code easier to read and maintain.

2. Step 2: Compare with other options

   Options A, B, and C describe unrelated concepts like styling, dynamic variables, or functions, which enums do not handle.

3. Final Answer:

   To group related constant values under a single name -> Option A

4. Quick Check:

   Enums = group constants [OK]

Hint: Enums group fixed values for clarity and safety [OK]

Common Mistakes:

• Thinking enums create dynamic or changeable variables
• Confusing enums with functions or styling
• Using enums for unrelated tasks like CSS

2. Which of the following is the correct syntax to declare an enum named UserRole with values Admin and User in Angular?

easy

A. UserRole enum { Admin, User }

B. enum UserRole = { Admin, User }

C. enum UserRole { Admin, User }

D. enum UserRole: { Admin, User }

Solution

1. Step 1: Recall enum declaration syntax in TypeScript

   The correct syntax is enum Name { Value1, Value2 } without equals or colons.

2. Step 2: Check each option

   enum UserRole { Admin, User } matches the correct syntax. Options B, C, and D use invalid symbols like '=', misplaced keywords, or colons.

3. Final Answer:

   enum UserRole { Admin, User } -> Option C

4. Quick Check:

   enum syntax = enum Name { ... } [OK]

Hint: Use 'enum Name { ... }' without '=' or ':' [OK]

Common Mistakes:

• Adding '=' after enum name
• Using ':' instead of braces
• Misplacing the 'enum' keyword

3. Given the enum declaration:

enum Status { Active = 1, Inactive = 0 }

What will be the output of console.log(Status.Active)?

medium

A. 1

B. Active

C. 0

D. undefined

Solution

1. Step 1: Understand enum value assignment

   Status.Active is explicitly assigned the value 1 in the enum.

2. Step 2: Check what console.log prints

   Logging Status.Active prints its numeric value, which is 1.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Enum value = number assigned [OK]

Hint: Enum member prints its assigned value [OK]

Common Mistakes:

• Expecting the name 'Active' to print instead of value
• Confusing 0 and 1 values
• Assuming undefined if not string

4. What is wrong with this enum declaration in Angular?

enum Color { Red = 'red', Green, Blue = 'blue' }

medium

A. Enum values cannot be strings

B. Enum names must be lowercase

C. Enum must have at least three values

D. You cannot mix string and numeric enum values without explicit assignment

Solution

1. Step 1: Analyze enum value types

   Mixing string and numeric enum members without explicit values causes errors.

2. Step 2: Identify the problem in the code

   Green has no assigned value after Red is string 'red', so it tries to auto-assign a number, which is invalid.

3. Final Answer:

   You cannot mix string and numeric enum values without explicit assignment -> Option D

4. Quick Check:

   Mixed enum types need explicit values [OK]

Hint: Assign all string values explicitly to avoid mixing errors [OK]

Common Mistakes:

• Assuming enum names must be lowercase
• Thinking enums can't have string values
• Believing enums require minimum count

5. You want to use an enum OrderStatus in Angular to represent these states: Pending, Shipped, Delivered, and Cancelled. You also want to display user-friendly text for each status in your template. Which approach is best?

hard

A. Use only strings in enum and display enum keys directly

B. Define enum with numeric values and create a mapping object for display text

C. Use separate string constants instead of enum

D. Use enum with mixed string and numeric values without mapping

Solution

1. Step 1: Understand enum usage for fixed states

   Using numeric enums keeps code efficient and clear for logic.

2. Step 2: Provide user-friendly text separately

   Mapping numeric enum values to display strings allows flexible, readable UI text.

3. Step 3: Evaluate other options

   Using only strings or constants reduces type safety or clarity; mixed enums without mapping cause errors.

4. Final Answer:

   Define enum with numeric values and create a mapping object for display text -> Option B

5. Quick Check:

   Numeric enum + mapping = best practice [OK]

Hint: Use numeric enums plus a display map for UI text [OK]

Common Mistakes:

• Using mixed enum types without mapping
• Displaying enum keys directly without user-friendly text
• Avoiding enums and using loose string constants