resequencer.js

/*

A toy implementation of the Resequencer pattern from Enterprise Integration Patterns.
https://www.enterpriseintegrationpatterns.com/patterns/messaging/Resequencer.html

*/

const createResequencer = (destination) => {
  const buffer = {};
  let next = 1;
  let last = -1;

  const consume = (message) => {
    addToBuffer(message);
    sendSequence();
  };

  const addToBuffer = (message) => {
    const sequenceNumber = message.sequenceNumber;
    buffer[sequenceNumber] = message;
    if (sequenceNumber > last) last = sequenceNumber;
  };

  const sendSequence = () => {
    if (next > last) return;
    if (!buffer[next]) return; 

    destination.push(buffer[next]);
    next = next + 1;

    sendSequence();
  };

  return { consume };
};

const destination = [];
const resequencer = createResequencer(destination);
const createMessage = (n) => ({
  sequenceNumber: n,
  payload: `Message with sequenceNumber: ${n}`
});

[2, 4, 3, 1, 7, 6, 5]
  .map(createMessage)
  .forEach(resequencer.consume);

console.log(destination);