Can someone explain first-class functions, higher-order functions, and closures in JavaScript?

Here’s one example that combines the ideas: `const makeAdder = amount => number => number + amount;`. `makeAdder` is a higher-order function because it returns another function. The returned function is first-class because it can be stored in a variable: `const addFive = makeAdder(5);`. It is also a closure because it remembers the `amount` value, so `addFive(10)` returns `15`. Try changing the values and logging each step in your browser’s developer tools.

The easiest way to learn these is by writing small exercises rather than memorizing definitions. Try passing callbacks to `map`, `filter`, and `setTimeout`, then write a function that returns another function. For closures, create a counter such as `const counter = () => { let value = 0; return () => ++value; };`. Each returned function remembers its own `value`. Use a debugger and inspect the variables while the functions run. Closures usually take more practice because they depend on scope and variable lifetime.

A useful distinction is that first-class functions describe what JavaScript allows you to do with functions, while higher-order functions describe a function’s behavior. First-class means a function can be handled as data. Higher-order means the function works with other functions. Closures describe how a function remembers variables from the scope where it was created. These aren’t three competing types of functions; one function can fit all three descriptions.

A first-class function is a function that JavaScript lets you treat like any other value. You can store it in a variable, pass it as an argument, or return it from another function. A higher-order function is a function that accepts another function, returns one, or does both. For example, `array.map(x => x * x)` is higher-order because `map` receives a function. A closure happens when an inner function keeps access to variables from the surrounding function, even after the outer function has finished running.