CommonJS vs ESM differences in Node.js - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the 'fs' module using CommonJS syntax.

Node.js

const fs = require([1]);

Drag options to blanks, or click blank then click option'

A'filesystem'

B'file-system'

C'fs'

D'Fs'

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect module names like 'file-system' or 'filesystem'.

Capitalizing the module name incorrectly.

In CommonJS, modules are imported using require() with the module name as a string. The correct module name for file system operations is 'fs'.

2fill in blank

medium

Complete the code to import the 'fs' module using ESM syntax.

Node.js

import fs from [1];

Drag options to blanks, or click blank then click option'

A'fs'

B'Fs'

C'filesystem'

D'file-system'

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect module names.

Forgetting to use quotes around the module name.

In ESM (ECMAScript Modules), you import modules using import with the module name as a string. The correct module name for the file system is 'fs'.

3fill in blank

hard

Fix the error in exporting a function named 'greet' using CommonJS syntax.

Node.js

module.exports = [1];

Drag options to blanks, or click blank then click option'

A{ greet }

Bfunction greet()

Cgreet()

Dgreet

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the function while exporting (e.g., greet()).

Exporting an object instead of the function directly.

In CommonJS, to export a function, you assign the function name (without parentheses) to module.exports. Using greet exports the function itself.

4fill in blank

hard

Fill both blanks to export a named function 'greet' using ESM syntax.

Node.js

[1] function greet() { console.log('Hello'); } [2]

Drag options to blanks, or click blank then click option'

Aexport

Bexport default

Cimport

Dmodule.exports

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'export default' for named exports.

Using CommonJS syntax like 'module.exports'.

In ESM, you export a named function by placing export before the function declaration. No extra export statement is needed after the function.

5fill in blank

hard

Fill all three blanks to import a named export 'greet' from 'greetings.js' using ESM syntax.

Node.js

import [1] from [2];

[3]();

Drag options to blanks, or click blank then click option'

A{ greet }

B'./greetings.js'

Cgreet

Dgreetings

Attempts:

3 left

💡 Hint

Common Mistakes

Importing without curly braces for named exports.

Forgetting quotes around the module path.

Calling the function with wrong name.

To import a named export in ESM, use curly braces around the name. The module path is a string with relative path. Then call the imported function by its name.

Practice

1. Which syntax is used to import modules in CommonJS in Node.js?

easy

A. const module = require('module')

B. import module from 'module'

C. module.import('module')

D. load('module')

Solution

1. Step 1: Understand CommonJS import syntax

   CommonJS uses the require function to import modules.

2. Step 2: Compare with other options

   Options A, B, and C are not valid CommonJS import syntax; B is ESM syntax.

3. Final Answer:

   const module = require('module') -> Option A

4. Quick Check:

   CommonJS imports use require() [OK]

Hint: CommonJS uses require(), ESM uses import [OK]

Common Mistakes:

• Confusing ESM import syntax with CommonJS
• Using import in CommonJS files
• Trying to use module.import() which doesn't exist

2. Which of the following is the correct way to export a function in ESM syntax?

easy

A. export = function() {}

B. module.exports = function() {}

C. exports.function = function() {}

D. export default function() {}

Solution

1. Step 1: Identify ESM export syntax

   ESM uses export default to export a default function or value.

2. Step 2: Eliminate CommonJS and invalid options

   module.exports = function() {} and C are CommonJS exports; D is invalid syntax.

3. Final Answer:

   export default function() {} -> Option D

4. Quick Check:

   ESM default export uses export default [OK]

Hint: ESM exports use export default or named export [OK]

Common Mistakes:

• Using module.exports in ESM files
• Trying to use export = which is invalid in ESM
• Confusing exports.function with ESM named exports

3. Given this CommonJS code, what will be the output?

const message = require('./message');
console.log(message);

And the file message.js contains:

module.exports = 'Hello from CommonJS';

medium

A. 'Hello from CommonJS'

B. undefined

C. SyntaxError

D. ReferenceError

Solution

1. Step 1: Understand module.exports in CommonJS

   The file exports a string 'Hello from CommonJS' using module.exports.

2. Step 2: Import and log the exported value

   The require call imports the string, so console.log prints it.

3. Final Answer:

   'Hello from CommonJS' -> Option A

4. Quick Check:

   CommonJS require returns module.exports value [OK]

Hint: require() returns module.exports value [OK]

Common Mistakes:

• Expecting require to return an object by default
• Confusing with ESM import behavior
• Thinking require throws error without .js extension

4. What is wrong with this ESM import statement in a Node.js file?

const fs = require('fs');

medium

A. Missing semicolon at the end

B. require is not defined in ESM modules

C. fs module cannot be imported in Node.js

D. Should use import fs from 'fs' instead

Solution

1. Step 1: Identify module system used

   The code uses require which is CommonJS syntax, but in ESM modules, require is not available.

2. Step 2: Understand ESM import rules

   ESM modules must use import statements; require is undefined.

3. Final Answer:

   require is not defined in ESM modules -> Option B

4. Quick Check:

   require() undefined in ESM [OK]

Hint: require() is undefined in ESM modules [OK]

Common Mistakes:

• Thinking require works in ESM without extra setup
• Confusing missing semicolon as error
• Believing fs cannot be imported in Node.js

5. You want to write a Node.js module that can be imported both by CommonJS and ESM users without errors. Which approach is best?

hard

A. Use module.exports and add a separate export default for ESM

B. Write only CommonJS syntax and use dynamic import() in ESM

C. Use a dual package approach with conditional exports in package.json

D. Write only ESM syntax and rename file to .mjs

Solution

1. Step 1: Understand compatibility challenges

   CommonJS and ESM have different import/export systems, so a single file often can't serve both seamlessly.

2. Step 2: Use Node.js dual package support

   Node.js supports conditional exports in package.json to provide separate entry points for CommonJS and ESM consumers.

3. Step 3: Evaluate other options

   Use module.exports and add a separate export default for ESM mixes syntaxes which doesn't work reliably, C requires dynamic import in consumers, D limits to ESM-only.

4. Final Answer:

   Use a dual package approach with conditional exports in package.json -> Option C

5. Quick Check:

   Dual package conditional exports solve CommonJS/ESM compatibility [OK]

Hint: Use package.json conditional exports for dual support [OK]

Common Mistakes:

• Trying to mix module.exports and export default in one file
• Using only .mjs files limits CommonJS users
• Relying on dynamic import() without package config