Default exports vs named exports in Typescript - Performance Comparison

Time Complexity: Default exports vs named exports

O(n)

Understanding Time Complexity

We want to see how the way we export code affects how long it takes to load or use modules.

How does choosing default or named exports change the work done when importing?

Scenario Under Consideration

Analyze the time complexity of importing modules using default and named exports.

// default export example
import myFunction from './module';

// named export example
import { myFunction } from './module';

// module.ts
export default function myFunction() { /* ... */ }
// export { myFunction }; // This line is incorrect and removed
export function helper() { /* ... */ }
    

This code shows two ways to import functions from a module: one uses a default export, the other uses named exports.

Identify Repeating Operations

Look at what happens when the module is imported.

• Primary operation: Module loading and symbol resolution.
• How many times: Once per import statement during program start or dynamic import.

How Execution Grows With Input

As the number of exports grows, the time to find the right export may increase.

Number of Exports (n)	Approx. Operations
10	10 lookups
100	100 lookups
1000	1000 lookups

Pattern observation: Finding a named export takes longer as exports increase; default export is a single direct reference.

Final Time Complexity

Time Complexity: O(n)

This means the time to find a named export grows linearly with the number of exports, while default export access is constant time.

Common Mistake

[X] Wrong: "Default and named exports have the same loading speed no matter how many exports exist."

[OK] Correct: Named exports require searching through all exports, so more exports mean more work; default export is a direct reference.

Interview Connect

Understanding how module exports affect loading helps you write efficient code and explain trade-offs clearly in interviews.

Self-Check

What if we used dynamic imports instead of static imports? How would the time complexity change?

Practice

1. What is the main difference between default export and named exports in TypeScript?

easy

A. Default export requires curly braces when importing, named exports do not.

B. Default export allows exporting one main value per file, named exports allow multiple exports by name.

C. Named exports can only export functions, default exports can only export objects.

D. Default exports are deprecated in TypeScript, named exports are preferred.

Solution

1. Step 1: Understand default export purpose

   Default export is designed to export a single main value from a file, like a main function or class.

2. Step 2: Understand named exports purpose

   Named exports allow exporting multiple values by their names, so you can import only what you need.

3. Final Answer:

   Default export allows exporting one main value per file, named exports allow multiple exports by name. -> Option B

4. Quick Check:

   Default export = one main, Named exports = multiple [OK]

Hint: Default = one main export, named = many exports by name [OK]

Common Mistakes:

• Confusing import syntax for default and named exports
• Thinking default export can export multiple items
• Assuming named exports require default keyword

2. Which of the following is the correct syntax to import a default export from a module named utils.ts?

easy

A. import utils from './utils';

B. import { utils } from './utils';

C. import * as utils from './utils';

D. import utils = require('./utils');

Solution

1. Step 1: Recall default import syntax

   Default exports are imported without curly braces using the syntax: import name from 'module'.

2. Step 2: Check options for correct syntax

   import utils from './utils'; matches this syntax exactly, importing the default export as utils.

3. Final Answer:

   import utils from './utils'; -> Option A

4. Quick Check:

   Default import has no braces [OK]

Hint: Default imports have no curly braces [OK]

Common Mistakes:

• Using curly braces for default imports
• Confusing import * as with default import
• Using require syntax in ES modules

3. Given the following module mathUtils.ts:

export default function add(a: number, b: number) { return a + b; }
export function multiply(a: number, b: number) { return a * b; }

What will be the output of this code?

import add, { multiply } from './mathUtils';
console.log(add(2, 3));
console.log(multiply(2, 3));

medium

A. NaN and 6

B. Syntax error

C. 5 and undefined

D. 5 and 6

Solution

1. Step 1: Understand import statements

   The default export function add is imported without braces, and the named export multiply is imported with braces.

2. Step 2: Evaluate function calls

   add(2, 3) returns 5, and multiply(2, 3) returns 6, so console logs 5 and 6.

3. Final Answer:

   5 and 6 -> Option D

4. Quick Check:

   Default + named import works = 5 and 6 [OK]

Hint: Default import no braces, named import with braces [OK]

Common Mistakes:

• Importing default export with braces
• Calling undefined functions due to wrong import
• Confusing output values

4. Consider this code snippet:

export default function greet() { return 'Hello'; }
export function greet() { return 'Hi'; }

What is the problem here?

medium

A. There is no problem; this code works fine.

B. Default export must be a variable, not a function.

C. You cannot have two functions with the same name exported, even if one is default.

D. Named exports cannot be functions.

Solution

1. Step 1: Identify duplicate function names

   Both the default export and named export use the same function name greet, which causes a conflict.

2. Step 2: Understand export rules

   Exports must have unique names; default export can be anonymous or named but cannot clash with named exports.

3. Final Answer:

   You cannot have two functions with the same name exported, even if one is default. -> Option C

4. Quick Check:

   Duplicate export names cause error [OK]

Hint: Default and named exports cannot share the same name [OK]

Common Mistakes:

• Assuming default export must be anonymous
• Thinking named exports can't be functions
• Ignoring duplicate export names

5. You have a file shapes.ts exporting multiple shapes and a default export for the main shape:

export interface Circle { radius: number; }
export interface Square { side: number; }
const defaultShape = { type: 'circle', radius: 5 };
export default defaultShape;

How would you import both the default shape and the Square interface correctly in another file?

hard

A. import defaultShape, { Square } from './shapes';

B. import { defaultShape, Square } from './shapes';

C. import { defaultShape } from './shapes'; import Square from './shapes';

D. import * as shapes from './shapes';

Solution

1. Step 1: Import default export without braces

   The default export defaultShape is imported without curly braces.

2. Step 2: Import named export with braces

   The named export Square interface is imported with curly braces.

3. Final Answer:

   import defaultShape, { Square } from './shapes'; -> Option A

4. Quick Check:

   Default no braces, named with braces [OK]

Hint: Default import no braces, named imports with braces [OK]

Common Mistakes:

• Using braces for default import
• Trying to import default as named
• Confusing import * as with default import