Module scope in Javascript - Time & Space Complexity

Time Complexity: Module scope

O(1)

Understanding Time Complexity

When we use modules in JavaScript, we want to know how the program's speed changes as the code grows.

We ask: How does the time to run code inside a module change with more code or imports?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

// module.js
export function greet(name) {
  return `Hello, ${name}!`;
}

// main.js
import { greet } from './module.js';
console.log(greet('Alice'));
    

This code defines a simple function in a module and uses it in another file.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Calling the greet function once.
• How many times: Exactly one time in this example.

How Execution Grows With Input

Since the function runs once, the time remains constant as code size grows.

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

Pattern observation: The time is constant regardless of input size.

Final Time Complexity

Time Complexity: O(1)

This means the execution time is constant for this operation inside the module.

Common Mistake

[X] Wrong: "Importing a module makes the program slower as the module size grows."

[OK] Correct: Importing just brings code in once; running functions inside the module costs time only when called.

Interview Connect

Understanding module scope time helps you explain how code organization affects performance in real projects.

Self-Check

"What if the greet function called another function inside the module multiple times? How would the time complexity change?"

Practice

1. What does module scope mean in JavaScript?

easy

A. All variables are global and accessible everywhere

B. Variables and functions are private to the file unless exported

C. Functions can only be used inside loops

D. Variables must be declared with var only

Solution

1. Step 1: Understand module scope concept

   Module scope means code inside a file is private unless explicitly shared.

2. Step 2: Compare options with this concept

   Only Variables and functions are private to the file unless exported correctly states variables/functions are private unless exported.

3. Final Answer:

   Variables and functions are private to the file unless exported -> Option B

4. Quick Check:

   Module scope = private unless exported [OK]

Hint: Remember: module code is private unless exported [OK]

Common Mistakes:

• Thinking all variables are global
• Confusing module scope with block scope
• Believing functions must be inside loops

2. Which of the following is the correct way to export a function named greet from a module?

easy

A. export function greet() {}

B. function export greet() {}

C. export greet() {}

D. export = greet()

Solution

1. Step 1: Recall correct export syntax

   To export a function, use export function functionName() {}.

2. Step 2: Check each option

   export function greet() {} matches the correct syntax; others are invalid or incorrect.

3. Final Answer:

   export function greet() {} -> Option A

4. Quick Check:

   Export function syntax = export function name() [OK]

Hint: Use 'export function' before function name [OK]

Common Mistakes:

• Placing export after function keyword
• Using incorrect export assignment syntax
• Missing parentheses in function declaration

3. Given this module code:

const secret = 42;
export const visible = 'hello';

console.log(typeof secret);
console.log(typeof visible);

What is the output when this module runs?

medium

A. "number" and "string"

B. "undefined" and "string"

C. "number" and "undefined"

D. ReferenceError for secret

Solution

1. Step 1: Understand variable scope and export

   Both secret and visible exist inside the module; secret is private, visible is exported.

2. Step 2: Check typeof outputs inside the same module

   Inside the module, both variables exist, so typeof secret is "number" and typeof visible is "string".

3. Final Answer:

   "number" and "string" -> Option A

4. Quick Check:

   typeof secret = number, typeof visible = string [OK]

Hint: Inside module, all declared variables exist [OK]

Common Mistakes:

• Thinking private variables are undefined inside module
• Confusing export with variable existence
• Expecting ReferenceError inside same file

4. What is wrong with this module code?

const count = 10;
export count = 20;

medium

A. Cannot export a variable twice

B. count is not declared before export

C. Syntax error: export cannot be used with assignment

D. No error, code works fine

Solution

1. Step 1: Analyze export syntax

   Export keyword cannot be used with assignment like export count = 20;. It must be export const count = 20; or export existing variables.

2. Step 2: Identify error type

   This causes a syntax error because export expects declaration or named export, not assignment.

3. Final Answer:

   Syntax error: export cannot be used with assignment -> Option C

4. Quick Check:

   Export syntax must declare or export existing variables [OK]

Hint: Export must declare or export, not assign [OK]

Common Mistakes:

• Trying to export by assignment
• Missing const/let/var with export
• Assuming export can change variable value

5. You have two modules:

// file1.js
const secret = 'hidden';
export const data = 123;

// file2.js
import { data } from './file1.js';
console.log(secret);
console.log(data);

What will happen when file2.js runs?

hard

A. Logs undefined and 123

B. Logs 'hidden' and 123

C. SyntaxError due to import

D. ReferenceError: secret is not defined

Solution

1. Step 1: Understand module scope and imports

   The variable secret is private to file1.js and not exported, so it cannot be accessed in file2.js.

2. Step 2: Predict runtime behavior

   Trying to access secret in file2.js causes a ReferenceError. The imported data logs correctly.

3. Final Answer:

   ReferenceError: secret is not defined -> Option D

4. Quick Check:

   Private variables cause ReferenceError outside module [OK]

Hint: Only exported variables are accessible in other modules [OK]

Common Mistakes:

• Assuming private variables are imported automatically
• Confusing import syntax errors with runtime errors
• Expecting undefined instead of ReferenceError