Namaste Node.js - Episode 4 Summary

Importing and Exporting in Node.js

Importing and Using

To import a function from a module, use the require function. Here's an example:

// In file app.js
const greet = require('./greet');
console.log(greet('World')); // Output: Hello, World!

Exporting Multiple Functions/Variables

To export multiple functions or variables, attach them to the module.exports object:

// In file utils.js
const add = (a, b) => a + b;
const subtract = (a, b) => a - b;

module.exports = { add, subtract };

Importing Multiple Exports

To import multiple exports from a module, use destructuring:

// In file app.js
const { add, subtract } = require('./utils');
console.log(add(5, 3));      // Output: 8
console.log(subtract(5, 3)); // Output: 2

How require Works

When you use require to import a module, Node.js executes the code in the module file. Only the properties of module.exports are exposed to the importing file.

Example:

// In file data.js
const secret = 'hidden';
const publicData = 'visible';

module.exports = publicData;

// In file app.js
const data = require('./data');
console.log(data); // Output: visible
console.log(secret); // Error: secret is not defined

In the example above, secret is not accessible outside data.js because it was not exported using module.exports.

.mjs vs. .cjs Modules

.cjs Modules (CommonJS)

• File Extension: .js or .cjs
• Module System: CommonJS
• Usage: require() and module.exports

Example:

// In file common.js
module.exports = function() { /* ... */ };

.mjs Modules (ES Modules)

• File Extension: .mjs
• Module System: ES Modules (ESM)
• Usage: import and export

Example:

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

Importing in .mjs

// In file app.mjs
import { greet } from './module.mjs';
console.log(greet('World')); // Output: Hello, World!

Differences Between .mjs and .cjs

• Syntax: .cjs uses require and module.exports, while .mjs uses import and export.
• Compatibility: .mjs is the standard ES Module syntax and is compatible with modern JavaScript, while .cjs is used for legacy Node.js modules.
• Use Case: Use .mjs for new projects or when using features of ES Modules, and .cjs for legacy code or when using the CommonJS module system.

Summary

• module.exports is used to export functions, objects, or variables from a module.
• require imports these exports into another module.
• .cjs modules use CommonJS syntax (require and module.exports), while .mjs modules use ES Module syntax (import and export).
• These kind of pattern used for import export in Nodejs