Skip to content

buffers.md

Latest commit

 

History

History
106 lines (67 loc) · 2.6 KB

buffers.md

File metadata and controls

106 lines (67 loc) · 2.6 KB
layout default
title Buffers in depth
url buffers
author john
date 2019-11-14

Buffers

Node's Buffer class enables working with binary data in JavaScript. A buffer allows a program to store data temporarily outside the V8 engine's stack.

Though not entirely accurate we can think of a buffer as an array of bytes, each byte is represented by a hexadecimal digit.

The Node Buffer class is a global class and therefore does not need to be imported into a module.

Example

In this first example, it creates a buffer from a string and shows some of the basic manipulation this provides.

// create a buffer from a string
const myBuffer = Buffer.from("hello node buffers");

console.log(myBuffer);
// <Buffer 68 65 6c 6c 6f 20 6e 6f 64 65 20 62 75 66 66 65 72 73>

console.log(myBuffer[0]);
// 104 - unicode char code for h (decimal representation of hex number 68)

console.log(myBuffer.toString());
// hello node buffers

Instantiating a Buffer

The Buffer.from() methods allows instantiated Buffers with:

  • a string
  • an array
  • another Buffer
  • an arrayBuffer
  • an object

Buffers can also be instantiated by size using Buffer.alloc(), Buffer.allocUnsafe() and Buffer.allocUnsafeSlow(). alloc allocates a new buffer of a given size, and fills it with zeros (or whatever is specified in the fill parameter. The allocUnsafe method allocates a given space in memory but does not initialise the values. The contents of the newly created block of memory are unknown, and they potentially may contain sensitive data.

Example

const myBuffer1 = Buffer.from([1, 2, 3]);
console.log(myBuffer1.length);
// 3

const myBuffer2 = Buffer.alloc(3);
console.log(myBuffer2);
// <Buffer 00 00 00>

// allocate a size for the buffer and give each byte an initial value 'a'
const myBuffer3 = Buffer.alloc(3, 'a');
console.log(myBuffer3);
// <Buffer 61 61 61>

Caveat: Buffer size

Once instantiated, using either from() or one of the alloc() methods a Buffer cannot be resized.

A Buffer's size is measured in bytes (common 8-bit bytes, or "Octets")'.

const myBuffer4 = Buffer.alloc(4);
console.log(myBuffer4);
// <Buffer 00 00 00 00>

myBuffer4.write('card');
console.log(myBuffer4);
// <Buffer 63 61 72 64>

myBuffer4.write('cards');
console.log(myBuffer4);
// <Buffer 63 61 72 64> - last character is lost

Terminology

Octet

An Octet is a more accurate way to describe a byte consisting of 8-bits. In some systems a byte can have more or less bits.