11. What is a higher order function?

A higher-order function in JavaScript is a function that either:

1. Takes another function as an argument
2. Returns a function as its result

Example 1: Taking a function as an argument

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function applyOperation(operation, a, b) {
  return operation(a, b);
}

function add(x, y) {
  return x + y;
}

console.log(applyOperation(add, 3, 5)); // Output: 8

Here, applyOperation is a higher-order function because it takes add (a function) as an argument.

Example 2: Returning a function

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

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

Here, multiplier is a higher-order function because it returns another function.

Common Higher-Order Functions in JavaScript:

Some built-in JavaScript functions are higher-order functions:

• map

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  const numbers = [1, 2, 3];
  const squared = numbers.map(n => n * n);
  console.log(squared); // Output: [1, 4, 9]
  

• filter

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  const numbers = [1, 2, 3, 4, 5];
  const evens = numbers.filter(n => n % 2 === 0);
  console.log(evens); // Output: [2, 4]
  

• reduce

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  const numbers = [1, 2, 3, 4];
  const sum = numbers.reduce((acc, curr) => acc + curr, 0);
  console.log(sum); // Output: 10
  

Why Use Higher-Order Functions?

• Code reusability: Functions can be passed as arguments to make code more modular.
• Better abstraction: They help break down complex problems into simpler functions.
• Functional programming: Encourages a cleaner and more declarative coding style.

Would you like more examples or explanations?