Simplified example of a data loss

test_message_loss_1.js

const {EventEmitter} = require('events');

const ee = new EventEmitter();

function waitForMessage() {
  return new Promise(resolve => {
    ee.once('message', msg => {
      console.log('waitForMessage. Message is received', msg);
      resolve();
      console.log('waitForMessage. Ooops, resolve will run in microtask. not immediately');
    });
  });
}

setTimeout(() => {
  console.log('emitting message #1');
  ee.emit('message', 'm1');
  console.log('emitting message #2');
  ee.emit('message', 'm2');
}, 1000);

(async () => {
  console.log('start of await #1');
  await waitForMessage();
  console.log('end of await #1');

  console.log('start of await #2');
  await waitForMessage();
  console.log('end of await #2');
})();

setInterval(() => {}, 1000);

/*
start of await #1
emitting message #1
waitForMessage. Message is received m1
waitForMessage. Ooops, resolve will run in microtask. not immediately
emitting message #2
end of await #1
start of await #2

// process hanged out
*/