What is a Buffer in Node.js? | Node.js Interview Questions

What You'll Learn

What Buffers are
Creating and using Buffers
Common operations

What is a Buffer?

Buffer is a temporary storage for binary data. Used when dealing with TCP streams, file operations, or any binary data.

Creating Buffers

code.jsJavaScript

// Create buffer from string
const buf1 = Buffer.from('Hello');

// Create empty buffer of size 10
const buf2 = Buffer.alloc(10);

// Create buffer with unsafe allocation (faster, not zeroed)
const buf3 = Buffer.allocUnsafe(10);

// From array
const buf4 = Buffer.from([72, 101, 108, 108, 111]);

Common Operations

code.jsJavaScript

const buf = Buffer.from('Hello World');

// Get length
console.log(buf.length); // 11

// Convert to string
console.log(buf.toString()); // 'Hello World'
console.log(buf.toString('hex')); // '48656c6c6f...'
console.log(buf.toString('base64')); // 'SGVsbG8gV29ybGQ='

// Slice buffer
const slice = buf.slice(0, 5);
console.log(slice.toString()); // 'Hello'

// Compare buffers
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('ABC');
console.log(buf1.equals(buf2)); // true

// Concatenate buffers
const combined = Buffer.concat([buf1, buf2]);

Use Case - Reading Binary File

code.jsJavaScript

const fs = require('fs');

fs.readFile('image.png', (err, buffer) => {
  console.log(buffer); // <Buffer 89 50 4e 47...>
  console.log(buffer.length); // file size in bytes
});