Convert a Node.js Readable

Edit on Github

Node.js APIs and npm packages often return a Node.js Readable rather than a web ReadableStream. The node:stream/consumers module collects one into any common type directly. This example shows each conversion.

import { Readable } from "node:stream";
import { blob, buffer, json, text } from "node:stream/consumers";

A helper that produces a fresh Readable for each conversion below, because a stream can only be read once.

function readableOf(content: string): Readable {
  return Readable.from([content]);
}

To collect into a string, use the text consumer.

console.log(await text(readableOf("Hello"))); // Hello

To parse the stream contents as JSON, use the json consumer.

const data = await json(readableOf('{"name":"Deno"}')) as { name: string };
console.log(data.name); // Deno

To collect into a Buffer, use the buffer consumer. Since a Buffer is a Uint8Array, this is also the route to bytes.

const bytes = await buffer(readableOf("Hello"));
console.log(bytes.length); // 5

To collect into a Blob, use the blob consumer. An ArrayBuffer is then one call away.

const asBlob = await blob(readableOf("Hello"));
console.log(asBlob.size); // 5

To get an array of the chunks, use the built-in toArray method.

const chunks = await readableOf("Hello").toArray();
console.log(chunks); // [ "Hello" ]

To convert to a web ReadableStream, use the static toWeb method. Web streams carry bytes, so the Readable should contain Uint8Array chunks. The reverse direction is Readable.fromWeb.

const byteReadable = Readable.from([new TextEncoder().encode("Hello")]);
const webStream = Readable.toWeb(byteReadable);
console.log(await new Response(webStream as ReadableStream).text()); // Hello

Run this example locally using the Deno CLI:

deno run https://docs.deno.com/examples/scripts/convert_node_readable.ts

Convert a Node.js Readable

Additional resources

Did you find what you needed?