What are Higher-Order Functions in JavaScript (HOF)

Higher-Order Function (HOF) is a function that takes another function as an argument or returns a function as a result.

Examples of Higher-Order Functions

Takes Another Function as Argument

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

function processUserInput(callback) {
  const name = "Alice";
  return callback(name);
}

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

Here processUserInput is a higher-order function since it takes another function greet as an argument.

Returns a Function

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

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

In this example multiplier returns another function — so it's also a higher-order function.

Where are Higher-Order Functions Used?

JavaScript actively uses HOF in built-in array methods: map, filter, reduce, forEach.

Example with map

const numbers = [1, 2, 3];
const doubled = numbers.map(num => num * 2);
console.log(doubled); // [2, 4, 6]

The map method is a higher-order function because it accepts another function (num => num * 2) as an argument.

Why are HOF Needed?

• Increase code flexibility and reusability
• Improve abstraction — you can write more general behavior not dependent on specific actions
• Allow implementing closures, decorators, partial application and other powerful concepts

Summary

Higher-order functions are functions that:

• Accept other functions as arguments
• Return functions as results
• Used extensively in functional programming and JavaScript