TypeScript Type Guards

When you're building a payment system, "close enough" isn't good enough. A single undefined value or a mismatched object property can be the difference between a successful transaction and a frustrated customer (or a lost sale). TypeScript's Type Guards are your first line of defense. They allow you to narrow down broad, uncertain types into specific ones that you can safely interact with. In this guide, we'll build a mini payment processor and learn how to use Type Guards to make it crash-proof. 1. The Problem: The "Silent Failures" of JavaScript Imagine you have a function that processes different types of payment responses. In plain JavaScript, you might write something like this: function processResponse(response) { // If response is a 'Success' object, it has a 'transactionId' // If it's an 'Error' object, it has a 'message' console.log("Payment successful! ID: " + response.transactionId); } // What if the API returned an error? processResponse({ message: "Insufficent funds" }); /