Synchronizer - basic synchronization using promise chaining

index.html

<script>
let synchronizer = Promise.resolve();

function synchronize(promiseFactory) {
  const promise = synchronizer.then(() => {
    return promiseFactory();
  });

  synchronizer = synchronizer.then(() => promise);

  return promise;
}

function timeout(milliseconds) {
  return new Promise((resolve) => {
    setTimeout(resolve, milliseconds);
  });
}

synchronize(() => {
  return timeout(300).then(function () {
    console.log('done with 300 ms timeout');
  });
});

synchronize(() => {
  return timeout(100).then(function () {
    console.log('done with 100 ms timeout');
  });
});
</script>