stream-encoding.js

const { Readable } = require("stream");

class ReadableTest extends Readable {
  constructor() {
    super({ highWaterMark: 256 });
    this.source = Buffer.from(`abcdefghijklmnopqrstuvwxyz..
The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog. 🚀`);
    this.pos = 0;
  }

  _read(size) {
    console.log("_read", size);
    let start = this.pos;
    let end = Math.min(start + size, this.source.length);
    this.pos = end;
    if (start < end) {
      console.log("push", end - start);
      this.push(this.source.slice(start, end));
    } else {
      console.log("push end");
      this.push(null);
    }
  }
}

function runTest(shouldSetEncoding) {
  return new Promise((resolve, reject) => {
    const readable = new ReadableTest();
    if (shouldSetEncoding) {
      readable.setEncoding("utf8");
    }
    let body = "";
    readable.on("data", chunk => {
      body += chunk;
      console.log("ondata body.length", body.length);
    });
    readable.on("error", reject);
    readable.on("end", () => resolve(body));
  });
}

async function main() {
  console.log("readable.on('data', chunk.toString()) without setEncoding");
  console.log(await runTest(false));
  console.log("readable.on('data', chunk) with setEncoding");
  console.log(await runTest(true));
}

main();