Hello readers 👋, welcome to the 7th of our Node.js journey! Last time, we explored how a single-threaded Node.js process magically handles thousands of requests at once. We saw that non-blocking I/O is the secret, and the event loop keeps everything spinning. But we left one critical question unanswered: how do we actually write the code that starts an async operation and then does something with the result? Today, we are going to dive into the two most fundamental ways to handle asynchronous code in Node.js: callbacks and promises . We'll see how callbacks work, why they can become messy, and how promises rescue us with cleaner, more readable code. Let's get into it. Why async code exists in Node.js We already know that Node.js uses a non-blocking model. When you call something like fs.readFile , you don't wait for the file to be fully loaded. Instead, you pass a function (a callback) that the event loop will run later, once the file content is ready. This pattern allows the main thread to stay responsive.…