&&, Lexical Scope, Closures, and Why Axios Feels Nicer Than fetch

One of those sessions where the JavaScript fundamentals get a little deeper. These concepts — scope, closures — are the kind of things that separate someone who uses JavaScript from someone who actually understands it. How && Actually Works in JavaScript Most people think && just returns true or false. It doesn't — it returns one of the actual values. Here's the full picture: If any value is falsy, it returns that falsy value and stops right there. Doesn't even look at the rest. If one is truthy and one is falsy, it returns the falsy one. If both are falsy, it returns the left side — because that's where it stopped. If both are truthy, it returns the right side — because it evaluated everything and the last truthy value wins. This is exactly why you see patterns like {isLoggedIn && <Dashboard />} in React. If isLoggedIn is false, && short-circuits and returns false — nothing renders. If it's true, && moves to the right side and returns — which renders. The whole conditional rendering p