json-seq-stream

application/json-seq / jsonl (NDJSON) support stream / async iterator library

This library provides composable TransformStream / ReadableWritablePair utilities to work with streaming JSON data formats.

Features

• [x] Supports RFC7464 (application/json-seq)
• [x] Supports JSON Lines / NDJSON (application/jsonl, application/x-ndjson)
• [x] Fully stream-compatible (Fetch API, File API, Bun/Deno, etc.)
• [x] Composable with standard Web Streams (pipeThrough())

Usage Examples

JSON Sequence (RFC 7464)

import { InputJsonSequenceStream } from "json-seq-stream";

type Value = { value: number };

const sequenceStream = new InputJsonSequenceStream<Value>();

const response = await fetch(url);
const readable = response.body!.pipeThrough(sequenceStream);

for await (const value of readable) {
  console.log(value);
}

JSON Lines / NDJSON

import { InputJsonLinesStream } from "json-seq-stream";

type Value = { value: number };

const linesStream = new InputJsonLinesStream<Value>();

const response = await fetch("https://example.com/data.jsonl");
const readable = response.body!.pipeThrough(linesStream);

for await (const value of readable) {
  console.log(value);
}

Output Example

import { OutputJsonLinesStream } from "json-seq-stream";

type Value = { value: number };

const { readable, writable } = new OutputJsonLinesStream<Value>();

const writer = writable.getWriter();
writer.write({ value: 1 });
writer.write({ value: 2 });
writer.close();

for await (const chunk of readable) {
  console.log(new TextDecoder().decode(chunk)); // NDJSON text lines
}

See also

• RFC 7464 - JavaScript Object Notation (JSON) Text Sequences
  https://datatracker.ietf.org/doc/html/rfc7464
• JSON Lines
  https://jsonlines.org
• JSON streaming - Wikipedia (en)
  https://en.wikipedia.org/wiki/JSON_streaming