chunk-data

Split buffers and streams into smaller chunks

Use case: When working with HTTP uploads and progress tracking, you need the request body to be sent in multiple chunks. However, data sources like Readable.from(buffer) emit the entire buffer as a single chunk, causing upload progress to jump from 0% to 100% instantly with no intermediate updates.

Install

npm install chunk-data

Usage

Chunking a buffer

import {chunk} from 'chunk-data';

const largeBuffer = new Uint8Array(10_000_000); // 10 MB

// Split into 64 KB chunks
for (const piece of chunk(largeBuffer, 65_536)) {
    console.log(piece.length);
    //=> 65536 (except last chunk)
}

Chunking an iterable of buffers

import {chunkFrom} from 'chunk-data';

const buffers = [new Uint8Array(1000), new Uint8Array(2000)];

// Re-chunk into 500-byte chunks
for (const piece of chunkFrom(buffers, 500)) {
    console.log(piece.length);
    //=> 500, 500, 500, 500, 500, 1000
}

Chunking a stream

import {chunkFromAsync} from 'chunk-data';
import {Readable} from 'node:stream';

const largeBuffer = new Uint8Array(10_000_000); // 10 MB
const stream = Readable.from([largeBuffer]);

// Split into 64 KB chunks
for await (const piece of chunkFromAsync(stream, 65_536)) {
    console.log(piece.length);
    //=> 65536 (except last chunk)
}

[!TIP] Node.js streams (like Readable) are async iterables and work directly with chunkFromAsync().

API

chunk(data, chunkSize)

Splits a typed array into smaller chunks.

This is a generator function that yields chunks of the specified size. Returns zero-copy views of the original buffer for optimal performance.

data

Type: ArrayBufferView

The typed array to split into chunks. Can be Uint8Array, Uint16Array, Int32Array, or any other typed array.

chunkSize

Type: number

The maximum size of each chunk in bytes. Must be a positive integer.

Returns: Generator<Uint8Array>

chunkFrom(iterable, chunkSize)

Splits an iterable of typed arrays into smaller chunks.

This is a generator function that re-chunks data from sources that emit inconsistently-sized chunks. Accumulates small chunks and splits large chunks to ensure consistent output chunk sizes.

iterable

Type: Iterable<ArrayBufferView>

The iterable of typed arrays to re-chunk. Can be an array of buffers, a generator, or any iterable that yields typed arrays.

chunkSize

Type: number

The maximum size of each chunk in bytes. Must be a positive integer.

Returns: Generator<Uint8Array>

chunkFromAsync(iterable, chunkSize)

Splits an async iterable of typed arrays into smaller chunks.

This async generator consumes an async iterable or iterable and re-emits its data as smaller chunks. Accumulates small chunks and splits large chunks to ensure consistent output chunk sizes.

iterable

Type: AsyncIterable<ArrayBufferView> | Iterable<ArrayBufferView>

The async iterable to read from and re-chunk. Can be any async iterable or iterable that yields typed arrays. Node.js streams are async iterables and work directly.

chunkSize

Type: number

The maximum size of each output chunk in bytes. Must be a positive integer.

Returns: AsyncGenerator<Uint8Array>

Why?

Problem: Upload progress tracking requires sending data in multiple chunks, but many data sources emit large single chunks:

import {Readable} from 'node:stream';

const buffer = new Uint8Array(10_000_000);
const stream = Readable.from([buffer]);

// This emits ONE chunk of 10 MB, not multiple smaller chunks
for await (const chunk of stream) {
    console.log(chunk.length);
    //=> 10000000 (entire buffer in one go)
}

Solution: Use chunkFromAsync() to split it:

import {Readable} from 'node:stream';
import {chunkFromAsync} from 'chunk-data';

const buffer = new Uint8Array(10_000_000);
const stream = Readable.from([buffer]);

// Now we get many smaller chunks
for await (const piece of chunkFromAsync(stream, 65_536)) {
    console.log(piece.length);
    //=> 65536
    //=> 65536
    //=> 65536
    //=> ... (152 chunks of 64 KB each, plus remainder)
}

This enables HTTP clients like Got to report incremental upload progress instead of jumping from 0% to 100%.

Performance

chunk() - Zero-copy views

Uses subarray() which creates views of the original data without copying. This means chunking is extremely fast and memory-efficient, even for large buffers.

import {chunk} from 'chunk-data';

const buffer = new Uint8Array(100_000_000); // 100 MB

for (const piece of chunk(buffer, 65_536)) {
    // No data copying - chunks are views into the original buffer
    // Chunking 100 MB takes <1ms
}

chunkFrom() and chunkFromAsync() - Optimized copying

May copy data to coalesce small input chunks, but optimized to minimize copying:

• Emit zero-copy views from large input chunks whenever possible
• Only copy when combining small chunks to reach the desired chunk size
• Avoid O(n²) behavior by copying at most once per input chunk

This makes them efficient for both scenarios:

• Sources that emit large chunks (mostly zero-copy)
• Sources that emit many small chunks (minimal copying)

When to use which?

• chunk() - When you have a single buffer in memory that you want to split into smaller pieces
• chunkFrom() - When you have multiple buffers (like an array or generator) that you want to re-chunk synchronously
• chunkFromAsync() - When you have a stream or async source that you want to re-chunk asynchronously

Related

• chunkify - Split an iterable into evenly sized chunks