Functions that call other functions — and why that's the foundation of everything async. Here's something that blew my mind when I first learned it: in JavaScript, functions are values . You can store them in variables, put them in arrays, pass them as arguments to other functions, and even return them from functions. That last one — passing a function as an argument — is the entire concept behind callbacks . And once you understand callbacks, you understand how setTimeout works, how addEventListener works, how array methods like map() and filter() work, and how JavaScript handles asynchronous operations. Callbacks are everywhere . I just didn't realize it until the ChaiCode Web Dev Cohort 2026 connected the dots. Let me show you what I mean. Functions Are Values in JavaScript Before we talk about callbacks, we need to establish this fundamental truth: functions in JavaScript are first-class citizens . That means they're treated just like any other value — numbers, strings, objects.…