@piadina/fetch-jsonl

Fetch Lines

Stream and parse (JSON Lines)[https://jsonlines.org/] directly with fetch. Yields parsed JSON objects one line at a time.

Install

npm install @piadina/fetch-jsonl

Usage

import fetchJSONLines from "@piadina/fetch-jsonl";

type Item = { id: number; name: string };

for await (const obj of fetchJSONLines<Item>("https://example.com/data.jsonl")) {
  console.log(obj.id, obj.name);
}

API

fetchJSONLines<T = unknown, TError extends Error = Error>(input: RequestInfo | URL, init?: RequestInit): AsyncGenerator<T>

• T – type of parsed objects (default unknown)
• TError – error type thrown on invalid JSON (default Error)
• input – fetch input (URL or Request)
• init – optional fetch init options

Returns an async generator that yields one parsed JSON object per line.

Example: Handling errors

try {
  for await (const obj of fetchJSONLines("https://example.com/data.jsonl")) {
    console.log(obj);
  }
} catch (err) {
  console.error("Invalid JSON line:", err);
}

Why JSON Lines?

• Works well for streaming APIs and large datasets
• You can start processing before the entire file downloads
• Friendly for incremental logs, events, and messages

Related

• JSONLines – spec