Enum member access in Typescript - Time & Space Complexity

Time Complexity: Enum member access

O(1)

Understanding Time Complexity

Let's see how fast we can get values from an enum in TypeScript.

We want to know how the time to access enum members changes as the enum grows.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

enum Colors {
  Red,
  Green,
  Blue,
  Yellow,
  Purple
}

const colorName = Colors[2];

This code gets the name of the color with the number 2 from the enum.

Identify Repeating Operations

• Primary operation: Direct lookup of enum member by key.
• How many times: Only once per access, no loops or repeated steps.

How Execution Grows With Input

Getting a value from an enum is like looking up a word in a dictionary.

Input Size (n)	Approx. Operations
10	1
100	1
1000	1

Pattern observation: The time to access an enum member stays the same no matter how many members there are.

Final Time Complexity

Time Complexity: O(1)

This means accessing an enum member takes the same short time, even if the enum is very big.

Common Mistake

[X] Wrong: "Accessing an enum member takes longer if the enum has more members."

[OK] Correct: Enum members are stored like keys in a map, so access is direct and fast regardless of size.

Interview Connect

Knowing that enum access is quick helps you explain how your code handles fixed sets of values efficiently.

Self-Check

"What if we used a function to search for a value inside an enum instead of direct access? How would the time complexity change?"

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