📍 What Does "First-Class Citizens" Mean?

In JavaScript, functions are first-class citizens. This means that functions are treated just like any other value — they can be:

1️⃣ Assigning Functions to Variables

const greet = function(name) {
  return "Hello, " + name;
};

console.log(greet("Alice")); // Hello, Alice

You can store a function in a variable just like you would store a number or string.

2️⃣ Passing Functions as Arguments

function sayHello() {
  console.log("Hello!");
}

function executeCallback(callback) {
  callback(); // invoke the function passed
}

executeCallback(sayHello);

You can pass functions into other functions as arguments. This is called a callback. 🔁

3️⃣ Returning Functions

function multiplier(factor) {
  return function(num) {
    return num * factor;
  };
}

const double = multiplier(2);
console.log(double(5)); // 10

This is an example of a higher-order function — a function that returns another function.

4️⃣ Functions in Arrays or Objects

Stored in an object:

const mathOps = {
  add: function(x, y) {
    return x + y;
  }
};

console.log(mathOps.add(2, 3)); // 5

Stored in an array:

const funcs = [
  () => console.log("One"),
  () => console.log("Two")
];

funcs[1](); // Two

⚙️ Real-World Use Case: setTimeout

setTimeout(function() {
  console.log("3 seconds later...");
}, 3000);

Here, an anonymous function is passed as a callback to setTimeout. It executes after 3 seconds. 🕒

🧠 Why This Matters

Because functions are first-class citizens:

✅ Summary

📚 Resources