nodejs-stream.md

tags
nodejs stream

Node.js stream

Ways to generate readable stream

• from other Node.js APIs that support streams(zlib, fs, http request/response, etc)
• Readable.from(string or Buffer | async function *)
• using readable.push:

const stream = require('node:stream');
const readable = new stream.Readable({ read() { } });

readable.push('First');
readable.push('Second');
readable.push(null); // null means end of stream

Ways to read from stream

Warning

Don't mix them up. Stick to one way that suits your codebase

• readable.on('data') - read chunk one by one
• readable.on('readable' - could be several chunks at once(null if the stream is ended)
• readable.pipe(writable)
• pipeline(for several streams):

const { pipeline } = require('node:stream/promises');
const fs = require('node:fs');
const zlib = require('node:zlib');

async function run() {
  const ac = new AbortController();
  const signal = ac.signal;

  setImmediate(() => ac.abort());
  await pipeline(
    fs.createReadStream('archive.tar'),
    zlib.createGzip(),
    fs.createWriteStream('archive.tar.gz'),
    { signal },
  );
}

run().catch(console.error); // AbortError

• AsyncIterable:

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

Advanced topics

• back-pressure(writable.cork(), readable.pause())
• stream supports AbortController and AbortSignal
• stream supports object-mode. Configures with readableObjectMode, writableObjectMode.

Code samples

https://github.com/HowProgrammingWorks/Streams/tree/master/JavaScript\