progressive-text-server.js

const http = require("http");

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

const server = http.createServer(async (req, res) => {
  res.writeHead(200, { "Content-Type": "text/plain; charset=UTF-8" });

  // Send enough padding to fill up the browser’s buffer
  res.write("\u200B".repeat(512));

  // Write the chunks one at a time
  for (var i = 0; i < 10; i++) {
    res.write(`[${i}] Hello, world!\n`);
    await sleep(1000);
  }
  res.end();
});

server.listen(8000);