mongo.js

// Let's say I have transaction code that looks like:

let state = 1;
session.withTransaction(async () => {
  // this can retry, which means otherFn can run twice and possible insert the wrong value or in the wrong order
  state++;
  await Promise.all([
    coll1.insertOne({ abc: 1 }, { session });
    otherFn(state, session),
  ])
});

async function otherFn(state, session) {
    // get some data from redis or another DB
    await setTimeout(Math.random() * 100);
    await coll2.insertOne({abc: state});
}