What is a buffer in Node.js?

Buffers in Node.js

A Buffer is a fixed-size chunk of memory allocated outside the V8 heap, used to work with binary data directly. Buffers are essential when dealing with streams, file I/O, network protocols, and encoding conversions.

Why Buffers?

JavaScript strings are UTF-16, which is great for text but wasteful for binary data (images, files, TCP packets). Buffers represent raw binary data as a sequence of bytes.

Creating Buffers

// From string
const buf1 = Buffer.from('Hello, Node.js!', 'utf8');

// From array of bytes
const buf2 = Buffer.from([72, 101, 108, 108, 111]);

// Allocate safe (zeroed) buffer
const buf3 = Buffer.alloc(10);          // 10 bytes, all zeros

// Allocate uninitialized (faster, but may contain old data)
const buf4 = Buffer.allocUnsafe(10);    // use with caution!

// From hex string
const buf5 = Buffer.from('48656c6c6f', 'hex');

Reading & Writing

const buf = Buffer.alloc(4);

// Write bytes
buf.writeUInt8(0x48, 0);   // 'H'
buf.writeUInt8(0x69, 1);   // 'i'

// Read bytes
console.log(buf[0]);        // 72
console.log(buf.toString('utf8')); // 'Hi'

// Inspect
console.log(buf.length);   // 4
console.log(buf);          // <Buffer 48 69 00 00>

Encoding Support

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

buf.toString('utf8');    // 'Hello'
buf.toString('hex');     // '48656c6c6f'
buf.toString('base64');  // 'SGVsbG8='
buf.toString('ascii');   // 'Hello'

Slicing & Copying

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

// slice references the same memory
const slice = buf.slice(0, 5);
console.log(slice.toString()); // 'Hello'

// copy creates a new buffer
const copy = Buffer.alloc(5);
buf.copy(copy, 0, 0, 5);
console.log(copy.toString()); // 'Hello'

// Modern: subarray (same as slice)
const sub = buf.subarray(7, 12);
console.log(sub.toString()); // 'World'

Buffers in Streams

const fs = require('fs');

fs.createReadStream('./image.png').on('data', (chunk) => {
  // chunk is a Buffer
  console.log(`Received ${chunk.length} bytes`);
});

Buffer vs TypedArray

Since Node.js 4, Buffer is a subclass of Uint8Array. You can use TypedArray methods on Buffer:

const buf = Buffer.from([1, 2, 3, 4, 5]);
const arr = new Uint8Array(buf);
// They share the same memory

Summary

Buffer = raw binary memory outside V8. Use it when handling binary protocols, file I/O, encryption, compression, or any data that isn't plain text. Always specify encoding when converting between Buffer and string.

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