String enums in Typescript - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing string enum member

What is the output of this TypeScript code?

Typescript

enum Direction {
  Up = "UP",
  Down = "DOWN",
  Left = "LEFT",
  Right = "RIGHT"
}

console.log(Direction.Left);

A "LEFT"

B Left

C 3

D undefined

💡 Hint

Remember that string enums store string values, not numbers.

The enum member Direction.Left is assigned the string "LEFT" explicitly, so logging it outputs "LEFT".

❓ Predict Output

intermediate

Value of enum member without explicit assignment

What will be the output of this TypeScript code?

Typescript

enum Status {
  Pending = "PENDING",
  Active,
  Completed = "COMPLETED"
}

console.log(Status.Active);

A 1

B "PENDING"

C undefined

D SyntaxError

💡 Hint

In string enums, all members must have string initializers.

In TypeScript, string enums require all members to have string values. Omitting the value for Active causes a syntax error.

🧠 Conceptual

advanced

Why use string enums over numeric enums?

Which of the following is the best reason to use string enums instead of numeric enums in TypeScript?

A String enums provide better readability and debugging because values are descriptive strings.

B String enums are faster to execute than numeric enums.

C String enums allow automatic reverse mapping from value to key.

D String enums consume less memory than numeric enums.

💡 Hint

Think about how values appear in logs and error messages.

String enums use descriptive string values which make code easier to read and debug compared to numeric enums which use numbers.

🔧 Debug

advanced

Identify the error in this string enum usage

What error will this TypeScript code produce?

Typescript

enum Colors {
  Red = "RED",
  Green = "GREEN",
  Blue = "BLUE"
}

const favorite: Colors = "RED";
console.log(favorite);

A No error, outputs "RED"

B ReferenceError: Colors is not defined

C Type '"RED"' is not assignable to type 'Colors'.

D TypeError: favorite is not a Colors enum

💡 Hint

Check the type compatibility between string literals and enum types.

You cannot assign a string literal directly to a variable typed as a string enum. The value must be Colors.Red.

🚀 Application

expert

Count enum members with string values

Given this string enum, how many members does it have?

Typescript

enum Fruits {
  Apple = "APPLE",
  Banana = "BANANA",
  Cherry = "CHERRY"
}

const count = Object.keys(Fruits).length;
console.log(count);

A 6

B 3

C 0

D undefined

💡 Hint

String enums do not create reverse mappings like numeric enums.

String enums only have keys for their members, so Object.keys returns the member names only, count is 3.

Practice

1. What is a key benefit of using string enums in TypeScript?

easy

A. They group related string constants under named values for clarity.

B. They automatically assign numeric values to members.

C. They allow mixing numbers and strings without errors.

D. They eliminate the need to declare enum members explicitly.

Solution

1. Step 1: Understand string enums purpose

   String enums group related string values under named constants to improve code clarity and safety.

2. Step 2: Compare options

   Only They group related string constants under named values for clarity. correctly describes this benefit. Numeric auto-assignment and mixing types are not features of string enums.

3. Final Answer:

   They group related string constants under named values for clarity. -> Option A

4. Quick Check:

   String enums improve clarity = A [OK]

Hint: String enums give names to strings for clearer code [OK]

Common Mistakes:

• Confusing string enums with numeric enums
• Thinking enum members can be implicit strings
• Assuming enums mix string and number types

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

easy

A. const enum Colors { Red = RED, Green = GREEN, Blue = BLUE }

B. enum Colors { Red, Green, Blue }

C. enum Colors { Red = 'RED', Green = 'GREEN', Blue = 'BLUE' }

D. enum Colors = { Red: 'RED', Green: 'GREEN', Blue: 'BLUE' }

Solution

1. Step 1: Review string enum syntax

   String enums require explicit string values assigned to each member using = 'value' inside an enum block.

2. Step 2: Check each option

   enum Colors { Red = 'RED', Green = 'GREEN', Blue = 'BLUE' } correctly uses enum Colors { Red = 'RED', ... }. enum Colors { Red, Green, Blue } lacks string assignments. enum Colors = { Red: 'RED', Green: 'GREEN', Blue: 'BLUE' } uses invalid syntax with = outside enum. const enum Colors { Red = RED, Green = GREEN, Blue = BLUE } misses quotes around string values.

3. Final Answer:

   enum Colors { Red = 'RED', Green = 'GREEN', Blue = 'BLUE' } -> Option C

4. Quick Check:

   String enum syntax = D [OK]

Hint: String enums need explicit string values with quotes [OK]

Common Mistakes:

• Omitting string values for enum members
• Using object literal syntax instead of enum
• Missing quotes around string values

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

enum Direction {
  Up = "UP",
  Down = "DOWN",
  Left = "LEFT",
  Right = "RIGHT"
}

console.log(Direction.Left);

medium

A. 3

B. "LEFT"

C. Left

D. undefined

Solution

1. Step 1: Understand enum member values

   Each member in the string enum has an explicit string value, e.g., Left = "LEFT".

2. Step 2: Check console.log output

   Logging Direction.Left prints the string value assigned, which is "LEFT".

3. Final Answer:

   "LEFT" -> Option B

4. Quick Check:

   Enum member value = "LEFT" [OK]

Hint: Enum member prints assigned string value, not name or index [OK]

Common Mistakes:

• Expecting member name instead of value
• Confusing string enums with numeric enums
• Assuming enum members print numeric indexes

4. Identify the error in this string enum declaration:

enum Status {
  Active = ACTIVE,
  Inactive = "INACTIVE"
}

medium

A. Enum name Status is invalid

B. Enum members cannot have different string values

C. Enum must use numeric values only

D. Missing quotes around ACTIVE in Active member

Solution

1. Step 1: Check string enum member values

   String enum members must have explicit string values in quotes, e.g., "ACTIVE".

2. Step 2: Identify error in Active member

   The Active member uses ACTIVE without quotes, causing a reference error.

3. Final Answer:

   Missing quotes around ACTIVE in Active member -> Option D

4. Quick Check:

   String values need quotes = A [OK]

Hint: Always put string enum values inside quotes [OK]

Common Mistakes:

• Forgetting quotes around string values
• Mixing string and numeric enum members
• Assuming enum names have restrictions

5. Given this string enum:

enum Role {
  Admin = "ADMIN",
  User = "USER",
  Guest = "GUEST"
}

Which code snippet correctly checks if a variable r is a valid Role value?

hard

A. if (Object.values(Role).includes(r)) { /* valid */ }

B. if (r in Role) { /* valid */ }

C. if (r === Role) { /* valid */ }

D. if (Role[r]) { /* valid */ }

Solution

1. Step 1: Understand enum value checking

   To check if r is a valid enum value, compare it against the enum's values, not keys.

2. Step 2: Evaluate each option

   if (Object.values(Role).includes(r)) { /* valid */ } uses Object.values(Role).includes(r), correctly checking if r matches any enum string value. if (r in Role) { /* valid */ } checks keys, not values. if (r === Role) { /* valid */ } compares a string to the enum object itself. if (Role[r]) { /* valid */ } tries to index enum with string value, which fails.

3. Final Answer:

   if (Object.values(Role).includes(r)) { /* valid */ } -> Option A

4. Quick Check:

   Check enum values with Object.values() = B [OK]

Hint: Use Object.values(enum).includes(value) to check string enums [OK]

Common Mistakes:

• Checking keys instead of values
• Comparing value directly to enum object
• Using enum indexing with string values