Node JS
Node JS
Node JS
Node JS

Node JS

Updated
Oct 19, 2023 02:57 PM
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Importing Modules: CommonJS / ES Modules

Compared to CommonJS, ES Modules allow you to import specific exports directly into your code, rather than importing the entire object and then accessing its properties.

CommonJS Imports

In CommonJS, the require() function is used to import a module. When you use require(), it returns the module.exports object from the imported module. This object contains all the exported values, functions, or objects that the module has provided.
Examples

Exporting a single function

File: add.js
function add(a, b) {
  return a + b;
}

module.exports = add;
File: main.js
const add = require('./add.js');
console.log(add(1, 2)); // Output: 3

Exporting multiple functions

File: math.js
function add(a, b) {
  return a + b;
}

function subtract(a, b) {
  return a - b;
}

module.exports = {
  add,
  subtract
};
File: main.js
const { add, subtract } = require('./math.js');
console.log(add(1, 2)); // Output: 3
console.log(subtract(1, 2)); // Output: -1

Exporting an object

File: config.js
const config = {
  port: 3000,
  apiUrl: 'https://api.example.com'
};

module.exports = config;
File: main.js
const config = require('./config.js');
console.log(config.port); // Output: 3000

ES Modules Imports

In ES Modules, the import and from keywords work together to import specific exports from a module:
  • The import keyword is used to declare the named exports or the default export you want to import. You can import named exports by placing their names inside curly braces ({}). To import the default export, you simply write the desired variable name without the curly braces.
  • The from keyword is followed by a string that specifies the path to the module you're importing from.
Examples

Example 1 - Exporting a single function

File: add.js
export function add(a, b) {
  return a + b;
}
File: main.js
import { add } from './add.js';
console.log(add(1, 2)); // Output: 3

Example 2 - Exporting multiple functions

File: math.js
export function add(a, b) {
  return a + b;
}

export function subtract(a, b) {
  return a - b;
}
File: main.js
import { add, subtract } from './math.js';
console.log(add(1, 2)); // Output: 3
console.log(subtract(1, 2)); // Output: -1

Example 3 - Exporting an object

File: config.js
export const config = {
  port: 3000,
  apiUrl: 'https://api.example.com'
};
File: main.js
import { config } from './config.js';
console.log(config.port); // Output: 3000

File Manipulation

FS module

The fs module provides an API for working with the file system. To get started, you need to require the fs module:
const fs = require('fs');

Reading files

Synchronous reading

To read a file synchronously, use the fs.readFileSync() method. This will block the execution of your program until the file is read.
const data = fs.readFileSync('example.txt', 'utf-8');
console.log('File content:', data);

Asynchronous reading

To read a file asynchronously, use the fs.readFile() method. This will not block the execution of your program and will utilize a callback function.
fs.readFile('example.txt', 'utf-8', (err, data) => {
  if (err) throw err;
  console.log('File content:', data);
});

Reading with streams

Reading with streams can be useful for processing large files efficiently. To read a file using a stream, use the fs.createReadStream() method:
const readStream = fs.createReadStream('example.txt', 'utf-8');

readStream.on('data', (chunk) => {
  console.log('Read chunk:', chunk);
});

readStream.on('end', () => {
  console.log('Finished reading the file');
});

readStream.on('error', (err) => {
  console.error('Error reading the file:', err);
});

Writing files

Synchronous writing

To write to a file synchronously, use the fs.writeFileSync() method.
const content = 'Hello, world!';
fs.writeFileSync('example.txt', content, 'utf-8');
console.log('File written successfully');

Asynchronous writing

To write to a file asynchronously, use the fs.writeFile() method.
const content = 'Hello, world!';
fs.writeFile('example.txt', content, 'utf-8', (err) => {
  if (err) throw err;
  console.log('File written successfully');
});

Writing with streams

Writing with streams is useful for processing large files or streaming data to a file. To write to a file using a stream, use the fs.createWriteStream() method:
const writeStream = fs.createWriteStream('example.txt', 'utf-8');

writeStream.write('Hello, world!');
writeStream.write('\nThis is another line.');

writeStream.end(() => {
  console.log('Finished writing the file');
});

writeStream.on('error', (err) => {
  console.error('Error writing the file:', err);
});

Deleting files

To delete a file, use the fs.unlink() method.
fs.unlink('example.txt', (err) => {
  if (err) throw err;
  console.log('File deleted successfully');
});

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