@portable/lines

Splits a stream of bytes or text into lines. Runs in browsers, Cloudflare Workers, Deno, Bun and Node 24+.

Replaces split2 and byline.

npm install @portable/lines

import * as Lines from '@portable/lines';
import * as Streams from '@portable/streams';
 
const response = await fetch('https://example.com/access.log');
const lines = response.body!.pipeThrough(new Lines.DecoderStream());
for await (const line of Streams.toAsyncIterable(lines)) {
  console.log(line);
}

Lines.DecoderStream is a TransformStream<Uint8Array | string, string>. Byte chunks are decoded with TextDecoder, so a multi-byte character split across chunks is decoded correctly, and a CRLF split across chunks counts as one line break.

Options

Types

Why use this over split2 and byline

split2 and byline are Node Transform streams. Lines.DecoderStream is a TransformStream, so it splits a fetch response body in any JavaScript runtime, and it has no dependencies outside @portable/*.

• It split 1.7 MB of text at the same speed as split2 in Node. node:readline was about 2× faster than both, but it exists only in Node.
• maxLength is checked on every line. split2 checks only the unfinished line at the end of each chunk, so whether it catches a long line depends on how the input was chunked.
• A multi-byte character or a CRLF split across two chunks is read as one character or one line break.
• Empty lines are kept by default, as in split2. byline drops them unless you pass keepEmptyLines, and skipEmpty: true drops them here.
• split2 takes a mapper function, such as split2(JSON.parse). Lines.DecoderStream has no mapper, so pipe its output through another TransformStream.
• byline splits on every Unicode line break by default. Pass separator: /\r\n|[\n\v\f\r\x85\u2028\u2029]/ for the same result.

Operations per second from pnpm bench, higher is better, in Node 24.22.0, on Intel(R) Xeon(R) Processor @ 2.10GHz (4 cores). A dash means the library has no equivalent.

Sizes cover the imports in the usage example, or the equivalent imports of each library, bundled for the browser by scripts/bundle-size.ts. Runtime dependencies count every package installed with the published package. A library that uses Node built-ins needs polyfills in a browser and the nodejs_compat flag in Cloudflare Workers.