jsonl-webstream

Lightweight library for JSON Lines web stream between browsers and Node.js environments

Overview

This library provides utilities for processing JSON Lines formatted data through the Web Streams API. It enables efficient streaming of JSON Lines data with minimal memory overhead across browsers and Node.js environments.

Installation

npm install jsonl-webstream

Usage

Reading JSON Lines

import { createJsonLinesReceiver } from 'jsonl-webstream';

// With fetch API
async function processJsonLines() {
  const response = await fetch('https://example.com/stream');
  const reader = response.body.getReader();
  const jsonlStream = createJsonLinesReceiver(reader);

  for await (const jsonData of jsonlStream) {
    // Process each JSON object
    console.log(jsonData);
  }
}

Writing JSON Lines

import { createJsonLinesSender } from 'jsonl-webstream';

function handleRequest(reply) {
  // Create a JSON Lines writer and its associated stream
  const { stream, writer } = createJsonLinesSender();

  writer.onCancel(() => {
    // when a client closed the response stream
  });

  // Set appropriate headers
  reply.type('application/jsonl');

  // Send the stream as the response
  reply.send(stream);

  // Write data as needed
  writer.write({ id: 1, message: "First item" });
  writer.write({ id: 2, message: "Second item" });

  // Close when done
  writer.close();
}

API Reference

Functions

createJsonLinesReceiver<T>(reader: ReadableStreamDefaultReader<Uint8Array>): ReadableStream<T>

Creates a ReadableStream that parses JSON Lines from a binary stream.

• Parameters:
  • reader: A ReadableStreamDefaultReader providing binary data
• Returns: A ReadableStream that emits parsed JSON objects of type T

createJsonLinesSender(): { stream: ReadableStream<Uint8Array>, writer: JsonLinesWriter }

Creates a paired ReadableStream and writer for JSON Lines streaming.

• Returns: An object containing:
  • stream: A binary ReadableStream that emits UTF-8 encoded JSON lines
  • writer: A JsonLinesWriter interface for sending JSON objects

Interfaces

JsonLinesWriter

Interface for writing JSON Lines data to a stream.

• Methods:
  • write(data: JsonValue): void - Writes a JSON value to the stream
  • close(): void - Closes the stream normally
  • onCancel(callback: () => void): void - Registers a callback for stream cancellation