9. What is a first class function?

What is a First-Class Function in JavaScript?

A first-class function means that functions in JavaScript are treated like any other value. This means:

✅ Functions can be assigned to variables
✅ Functions can be passed as arguments to other functions
✅ Functions can be returned from other functions
✅ Functions can be stored in data structures (like arrays, objects)

Examples of First-Class Functions

1. Assigning a Function to a Variable

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const greet = function(name) {
  return `Hello, ${name}!`;
};

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

2. Passing a Function as an Argument (Callback Function)

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function sayHello(callback) {
  console.log(callback("Bob"));
}

sayHello(name => `Hello, ${name}!`); // "Hello, Bob!"

3. Returning a Function from Another Function

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

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

4. Storing Functions in an Array

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const operations = [
  num => num + 1,
  num => num * 2,
  num => num ** 2
];

console.log(operations 8 (calls the second function)

5. Storing Functions in an Object

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const mathOperations = {
  add: (a, b) => a + b,
  multiply: (a, b) => a * b
};

console.log(mathOperations.add(3, 7)); // 10
console.log(mathOperations.multiply(4, 5)); // 20

Why Are First-Class Functions Useful?

✔ Higher-Order Functions – Functions that take other functions as arguments or return functions
✔ Functional Programming – Enables techniques like map, filter, reduce
✔ Callbacks & Event Handling – Used in async operations and event listeners

Would you like more real-world examples of first-class functions? 🚀