Binary I/O
Representing binary payloads in streams, files, and network protocols.
Node.js · Module
node:buffer
The node:buffer module provides Buffer, Node.js’s fixed-length byte sequence for handling binary data. It extends Uint8Array and supports safe allocation, conversion, encoding, and byte-level operations.
How it works
The module provides Buffer, a fixed-size byte sequence represented as a Uint8Array subclass. Create buffers from strings, arrays, ArrayBuffers, or other buffers, then use its methods to inspect, transform, encode, decode, and compare binary data.
Syntax
import { Buffer } from 'node:buffer';Parameters
| Name | Type | Description |
|---|---|---|
value | string | ArrayLike<number> | ArrayBuffer | Buffer | Input data such as a string, array, ArrayBuffer, or existing Buffer, depending on the factory used. |
size | integer | Number of bytes for allocation methods. |
encoding | string | Text encoding used when converting strings to or from bytes. |
Returns
Buffer instances containing copied data, initialized allocated bytes, or a view over ArrayBuffer memory, depending on the API used.
Key points
- Buffer is Node.js’s primary representation for fixed-size binary data.
- Buffer inherits typed-array capabilities while adding Node.js-specific binary-data operations.
- Creating a Buffer from another Buffer produces independent copied contents.
- Creating a Buffer from an ArrayBuffer can produce a shared-memory view instead of a copy.
Common mistakes
- Buffer follows Uint8Array behavior, so it is a typed-array view over binary data rather than a resizable collection.
- A requested allocation has a fixed byte length; it cannot grow dynamically.
Example: Encode text as bytes
import { Buffer } from 'node:buffer';
const input = 'hello';
const encoded = Buffer.from(input, 'utf8');
console.log(encoded.length);
console.log(encoded.toString('base64'));Creates a byte buffer from UTF-8 text and prints its byte length and Base64 representation.
When to use it
Encoding and decoding
Converting text or structured byte values to encoded data.
Typed-array interoperability
Working with typed-array and ArrayBuffer-based APIs.
Interview questions
QWhat is a Node.js Buffer?
Buffer represents a fixed-length sequence of bytes and extends Uint8Array with Node-specific methods. It is used by many Node.js APIs for binary data.
Follow-up: How can text be converted to a Buffer? Use Buffer.from(string, encoding), choosing the encoding explicitly when it is not UTF-8.
QHow do Buffer.from(), Buffer.alloc(), and Buffer.allocUnsafe() differ?
Buffer.from() creates a buffer from existing data, while Buffer.alloc() creates a specified-size buffer that is initialized safely. Buffer.allocUnsafe() can be faster but requires the contents to be overwritten or initialized before use.
Follow-up: When is allocUnsafe acceptable? Only when every byte will be deliberately initialized before the buffer can be observed.
QWhen does creating a Buffer copy data versus share memory?
Buffer.from(buffer) copies the source buffer's contents into a new Buffer. Buffer.from(arrayBuffer) instead creates a Buffer that shares the ArrayBuffer's memory, optionally using an offset and length.
Follow-up: What consequence follows from shared memory? Changes through either view can affect the same underlying bytes, so ownership must be managed carefully.
Related
Buffer.from()Buffer.alloc()Buffer.allocUnsafe()buf.toString()Uint8Arraybuffer.constants