Why enums are needed in Typescript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an enum named Direction.

Typescript

enum Direction {
  Up = [1],
  Down,
  Left,
  Right
}

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

A0

B1

Ctrue

D"UP"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values instead of numbers without explicit string enums.

Starting enum values at 1 without specifying.

Enums start numbering from 0 by default unless specified otherwise.

2fill in blank

medium

Complete the code to access the enum value for Direction.Left.

Typescript

const leftValue = Direction.[1];

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

ADown

BRight

CUp

DLeft

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or misspelled enum member names.

Trying to access enum values by number directly.

You access enum members by their names, like Direction.Left.

3fill in blank

hard

Fix the error in the enum declaration by completing the missing part.

Typescript

enum Status {
  Active = [1],
  Inactive,
  Pending
}

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

A"active"

B1

Ctrue

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values without quotes.

Using boolean values in enums.

Enum numeric values must be numbers. Using 1 starts numbering from 1.

4fill in blank

hard

Fill both blanks to create a function that returns a string based on enum input.

Typescript

function getStatusMessage(status: Status): string {
  switch(status) {
    case Status.Active:
      return [1];
    case Status.Inactive:
      return [2];
    default:
      return "Unknown";
  }
}

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

A"User is active"

B"User is inactive"

C"Active"

D"Inactive"

Attempts:

3 left

💡 Hint

Common Mistakes

Returning enum names instead of messages.

Mixing up messages for statuses.

The function returns descriptive messages for each enum status.

5fill in blank

hard

Fill all three blanks to create a numeric enum and use it in a condition.

Typescript

enum Level {
  Low = [1],
  Medium,
  High
}

const currentLevel = Level.[2];

if (currentLevel > Level.[3]) {
  console.log("Level is above Low");
}

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

A0

BMedium

CLow

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values instead of numbers in numeric enums.

Comparing enum values incorrectly.

The enum starts at 0 for Low, Medium is next, and the condition checks if currentLevel is above Low.

Practice

1. Why are enums useful in TypeScript?
enum Color { Red, Green, Blue }

easy

A. They group related values with readable names.

B. They allow dynamic addition of new values at runtime.

C. They replace all functions in TypeScript.

D. They automatically convert numbers to strings.

Solution

1. Step 1: Understand what enums represent

   Enums group a fixed set of related values under friendly names, improving code clarity.

2. Step 2: Analyze the options

   Only They group related values with readable names. correctly describes enums' purpose. Options A, B, and C are incorrect features.

3. Final Answer:

   They group related values with readable names. -> Option A

4. Quick Check:

   Enums improve readability = D [OK]

Hint: Enums group fixed options with names, not dynamic values [OK]

Common Mistakes:

• Thinking enums allow adding values at runtime
• Confusing enums with functions
• Believing enums convert numbers to strings automatically

2. Which of the following is the correct syntax to declare an enum in TypeScript?

easy

A. enum Direction { Up, Down, Left, Right }

B. enum Direction = (Up, Down, Left, Right);

C. enum Direction: [Up, Down, Left, Right];

D. enum Direction { 'Up', 'Down', 'Left', 'Right' }

Solution

1. Step 1: Recall enum declaration syntax

   In TypeScript, enums are declared using the keyword enum followed by curly braces with comma-separated names.

2. Step 2: Check each option

   enum Direction { Up, Down, Left, Right } matches the correct syntax. Options A and C use invalid assignment or colon syntax. enum Direction { 'Up', 'Down', 'Left', 'Right' } incorrectly uses quotes around names.

3. Final Answer:

   enum Direction { Up, Down, Left, Right } -> Option A

4. Quick Check:

   Correct enum syntax uses braces and names without quotes = B [OK]

Hint: Enums use braces and names without quotes [OK]

Common Mistakes:

• Using equals sign or colon instead of braces
• Putting quotes around enum member names
• Ending enum declaration with semicolon incorrectly

3. What will be the output of this TypeScript code?

enum Status { Active = 1, Inactive, Pending }
console.log(Status.Inactive);

medium

A. Inactive

B. 1

C. 0

D. 2

Solution

1. Step 1: Understand enum numeric values

   The enum starts with Active = 1, so Inactive gets the next number, 2, and Pending gets 3.

2. Step 2: Check the logged value

   Logging Status.Inactive prints its numeric value, which is 2.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Enum auto-increments numbers = A [OK]

Hint: Enum numbers auto-increment from first assigned value [OK]

Common Mistakes:

• Assuming enum starts at 0 when first value is assigned 1
• Expecting string output instead of number
• Confusing enum member names with their values

4. Identify the error in this enum declaration:

enum Size {
  Small = 'S',
  Medium = 'M',
  Large = 3
}

medium

A. Enum values must be unique numbers only.

B. Mixing string and number values in one enum is not allowed.

C. Enum member names must be lowercase.

D. Missing semicolon after enum declaration.

Solution

1. Step 1: Check enum value types

   TypeScript enums can be numeric or string, but mixing both types in one enum causes errors.

2. Step 2: Analyze the given enum

   Here, 'Small' and 'Medium' have string values, but 'Large' has a number, which is invalid.

3. Final Answer:

   Mixing string and number values in one enum is not allowed. -> Option B

4. Quick Check:

   Enum values must be consistent type = C [OK]

Hint: Enum values must be all strings or all numbers [OK]

Common Mistakes:

• Thinking enum member names must be lowercase
• Believing enum values must be unique numbers only
• Assuming missing semicolon causes error

5. You want to represent fixed user roles in your app: 'Admin', 'Editor', and 'Viewer'. Why is using an enum better than plain strings?

enum UserRole { Admin, Editor, Viewer }

hard

A. Enums automatically encrypt role names for security.

B. Enums allow adding new roles dynamically at runtime.

C. Enums prevent typos and make code easier to maintain.

D. Enums convert roles to numbers for faster database storage.

Solution

1. Step 1: Understand the benefit of enums for fixed sets

   Enums provide named constants that prevent typos and improve readability and maintainability.

2. Step 2: Evaluate the options

   Enums prevent typos and make code easier to maintain. correctly states the main advantage. Options B, C, and D describe incorrect or unrelated features.

3. Final Answer:

   Enums prevent typos and make code easier to maintain. -> Option C

4. Quick Check:

   Enums improve safety and clarity = A [OK]

Hint: Enums reduce errors by using fixed named values [OK]

Common Mistakes:

• Believing enums add dynamic behavior
• Thinking enums provide encryption
• Assuming enums optimize database storage automatically