String enums in Typescript - Time & Space Complexity

Time Complexity: String enums

O(n)

Understanding Time Complexity

We want to understand how the time it takes to use string enums changes as we work with more enum values.

How does the program's work grow when we look up or compare enum values?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

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

    function isPrimaryColor(color: string): boolean {
      return color === Colors.Red || color === Colors.Green || color === Colors.Blue;
    }
    

This code checks if a given string matches one of the string enum values.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Comparing the input string to each enum value.
• How many times: Once for each enum member (3 times here).

How Execution Grows With Input

Each time we add a new enum value, the function compares the input to one more string.

Input Size (n)	Approx. Operations
3	3 comparisons
10	10 comparisons
100	100 comparisons

Pattern observation: The number of comparisons grows directly with the number of enum values.

Final Time Complexity

Time Complexity: O(n)

This means the time to check grows in a straight line as the number of enum values grows.

Common Mistake

[X] Wrong: "Checking a string enum value is always instant no matter how many values there are."

[OK] Correct: Each check compares the input to every enum value one by one, so more values mean more work.

Interview Connect

Understanding how operations grow with input size helps you explain your code's efficiency clearly and confidently.

Self-Check

"What if we stored enum values in a Set and checked membership instead? How would the time complexity change?"

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