Enum member access in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the enum member.

Typescript

enum Color { Red, Green, Blue }
const favorite = Color.[1];

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

AYellow

BRed

CPink

DOrange

Attempts:

3 left

💡 Hint

Common Mistakes

Using a name not declared in the enum.

Trying to access enum members as strings.

The enum member Red is accessed using Color.Red.

2fill in blank

medium

Complete the code to get the numeric value of the enum member.

Typescript

enum Direction { Up = 1, Down, Left, Right }
const dirValue = Direction.[1];

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

AUp

BSideways

CBackward

DForward

Attempts:

3 left

💡 Hint

Common Mistakes

Using a member name not in the enum.

Confusing string values with numeric enum values.

The enum member Up has the numeric value 1, accessed by Direction.Up.

3fill in blank

hard

Fix the error in accessing the enum member.

Typescript

enum Status { Active = 'ACTIVE', Inactive = 'INACTIVE' }
const currentStatus = Status.[1];

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

AInactivee

Bactive

CACTIVE

DInactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or uppercase strings instead of enum member names.

Misspelling the enum member name.

Enum members are case-sensitive. The correct member is Inactive, not active or ACTIVE.

4fill in blank

hard

Fill both blanks to access the enum member and get its value.

Typescript

enum Fruit { Apple = 5, Banana = 10 }
const fruitName = Fruit.[1];
const fruitValue = Fruit.[2];

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

AApple

BBanana

COrange

DGrape

Attempts:

3 left

💡 Hint

Common Mistakes

Using names not declared in the enum.

Mixing up member names and values.

Fruit.Apple and Fruit.Banana access the enum members correctly.

5fill in blank

hard

Fill all three blanks to create an enum, access a member, and get its value.

Typescript

enum Vehicle { [1] = 1, [2] = 2, [3] = 3 }
const myVehicle = Vehicle.Car;

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

ACar

BBike

CTruck

DPlane

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid or duplicate member names.

Not assigning values to enum members.

The enum members are Car, Bike, and Truck. They are assigned values 1, 2, and 3 respectively.

Practice

1.

Which of the following is the correct way to access a member named Red from an enum called Color?

easy

A. Color.Red

B. Red.Color

C. Color[Red]

D. Red.Color()

Solution

1. Step 1: Understand enum member access syntax

   In TypeScript, enum members are accessed using dot notation with the enum name first, then the member name.

2. Step 2: Apply correct syntax to the example

   For enum Color and member Red, the correct access is Color.Red.

3. Final Answer:

   Color.Red -> Option A

4. Quick Check:

   Enum member access = Color.Red [OK]

Hint: Use EnumName.Member to access enum values quickly [OK]

Common Mistakes:

• Reversing the order like Red.Color
• Using brackets without quotes for string enums
• Calling enum members as functions

2.

Which of the following is the correct syntax to define a numeric enum named Direction with members Up, Down, Left, and Right?

?

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 the name and curly braces containing members.

2. Step 2: Match correct syntax

   enum Direction { Up, Down, Left, Right } uses enum Direction { Up, Down, Left, Right }, which is the correct syntax.

3. Final Answer:

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

4. Quick Check:

   Enum declaration uses curly braces {} [OK]

Hint: Use curly braces {} after enum name to list members [OK]

Common Mistakes:

• Using equals sign (=) after enum name
• Using colon (:) instead of braces
• Using parentheses () instead of braces

3.

Given the enum:

enum Status { Active = 1, Inactive, Pending }

What is the output of console.log(Status[2])?

medium

A. "Pending"

B. "Inactive"

C. 2

D. undefined

Solution

1. Step 1: Understand numeric enum reverse mapping

   Numeric enums in TypeScript create a reverse mapping from value to name. Here, Active = 1, so Inactive is 2, Pending is 3.

2. Step 2: Access enum member by value

   Status[2] returns the name of the member with value 2, which is Inactive.

3. Final Answer:

   "Inactive" -> Option B

4. Quick Check:

   Numeric enum reverse lookup = "Inactive" [OK]

Hint: Numeric enums map values back to names automatically [OK]

Common Mistakes:

• Assuming string enums have reverse mapping
• Confusing member names with values
• Expecting numeric output instead of string

4.

Consider this enum and code snippet:

enum Fruit { Apple = "APPLE", Banana = "BANANA" }
console.log(Fruit["APPLE"]);

What will happen when this code runs?

medium

A. undefined

B. "APPLE"

C. "Apple"

D. SyntaxError

Solution

1. Step 1: Understand string enum member access

   String enums do not have reverse mapping from value to name like numeric enums.

2. Step 2: Analyze the code behavior

   Accessing Fruit["APPLE"] looks for a member named "APPLE", but enum keys are "Apple" and "Banana". So it returns undefined.

3. Final Answer:

   undefined -> Option A

4. Quick Check:

   String enums lack reverse mapping = undefined [OK]

Hint: String enums do not support reverse lookup by value [OK]

Common Mistakes:

• Expecting reverse mapping for string enums
• Confusing enum keys with values
• Assuming case-insensitive access

5.

You have this enum and function:

enum Status { Success = 200, NotFound = 404, ServerError = 500 }

function getStatusName(code: number): string {
  return Status[code] || "Unknown";
}

What will getStatusName(404) return, and why?

hard

A. "Unknown" because reverse mapping is not supported

B. "404" because it returns the number as string

C. Runtime error due to invalid access

D. "NotFound" because numeric enums support reverse mapping

Solution

1. Step 1: Recognize numeric enum reverse mapping

   Numeric enums in TypeScript create a reverse mapping from numeric values to member names.

2. Step 2: Evaluate function behavior with input 404

   Calling getStatusName(404) returns Status[404], which is "NotFound". If no match, it returns "Unknown".

3. Final Answer:

   "NotFound" because numeric enums support reverse mapping -> Option D

4. Quick Check:

   Numeric enum reverse lookup returns member name [OK]

Hint: Numeric enum values map back to names automatically [OK]

Common Mistakes:

• Thinking it returns the number as string
• Assuming reverse mapping doesn't exist
• Expecting runtime errors on valid enum access