Example of reporting on progress using an async generator function and websockets

socketreporter.js

const WebSocket = require('ws');

// Core solver logic, stubbed out for example
async function* slow() {
  yield 'starting...';
  await new Promise(resolve => setTimeout(resolve, 10 * 1000));

  // Use `yield` to report on progress
  yield 'loading data...';
  await new Promise(resolve => setTimeout(resolve, 10 * 1000));

  yield 'running solver engine...';
  await new Promise(resolve => setTimeout(resolve, 10 * 1000));

  return { answer: 42 };
}

// WebSocket server
const server = new WebSocket.Server({
  port: 8080
});

server.on('connection', function(socket) {
  socket.on('message', async function(msg) {
    if (msg !== 'solve') { return; }

    const generator = slow();
    let done = false;
    while (!done) {
      const next = await generator.next();
      done = next.done;
      socket.send(JSON.stringify(next));
    }
  });
});

// WebSocket client
const client = new WebSocket('ws://localhost:8080');

client.once('open', function() {
  client.on('message', msg => {
    msg = JSON.parse(msg);
    console.log(new Date(), msg.value);
    if (msg.done) {
      client.close();
    }
  });

  client.send('solve');
});