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Streams

The Node.js streams API ↗ is the original API for working with streaming data in JavaScript, predating the WHATWG ReadableStream standard ↗. A stream is an abstract interface for working with streaming data in Node.js. Streams can be readable, writable, or both. All streams are instances of EventEmitter.

Where possible, you should use the WHATWG standard "Web Streams" API ↗, which is supported in Workers ↗.

import {
  Readable,
  Transform,
} from 'node:stream';


import {
  text,
} from 'node:stream/consumers';


import {
  pipeline,
} from 'node:stream/promises';


// A Node.js-style Transform that converts data to uppercase
// and appends a newline to the end of the output.
class MyTransform extends Transform {
  constructor() {
    super({ encoding: 'utf8' });
  }
  _transform(chunk, _, cb) {
    this.push(chunk.toString().toUpperCase());
    cb();
  }
  _flush(cb) {
    this.push('\n');
    cb();
  }
}


export default {
  async fetch() {
    const chunks = [
      "hello ",
      "from ",
      "the ",
      "wonderful ",
      "world ",
      "of ",
      "node.js ",
      "streams!"
    ];


    function nextChunk(readable) {
      readable.push(chunks.shift());
      if (chunks.length === 0) readable.push(null);
      else queueMicrotask(() => nextChunk(readable));
    }


    // A Node.js-style Readable that emits chunks from the
    // array...
    const readable = new Readable({
      encoding: 'utf8',
      read() { nextChunk(readable); }
    });


    const transform = new MyTransform();
    await pipeline(readable, transform);
    return new Response(await text(transform));
  }
};

Refer to the Node.js documentation for stream ↗ for more information.

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