Thoughts.

mongo-db-syncer is a small Go CLI that copies every collection from one database to another in the same cluster, using MongoDB's own $out stage instead of streaming documents through the app.

Generator functions pause and resume on yield instead of running top to bottom. A basic introduction to how .next() drives that, and why it makes implementing an iterable almost trivial.

Before Promises, Javascript leaned on nested callbacks for async work. A walk through why callback hell happens, what the Promise constructor actually does, and why "I will be logged first" beats "Hello world" to the console.