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# Higher-Order Functions (HOFs) in JavaScript: A Comprehensive Guide π

### Higher-Order Functions (HOFs) in JavaScript: A Comprehensive Guide π

Higher-order functions (HOFs) are a powerful feature in JavaScript that can make your code more modular, reusable, and expressive. This article will delve into the concept of HOFs, explain why they are useful, and provide practical examples to help you understand how to use them effectively. Let's get started! π

#### What are Higher-Order Functions? π€

In JavaScript, a higher-order function is a function that either:

• Takes one or more functions as arguments, or
• Returns a function as its result.

This ability allows for more flexible and concise code, especially when dealing with operations on collections of data.

#### Why Use Higher-Order Functions? π

Higher-order functions can simplify your code by:

• Reducing redundancy
• Enhancing modularity

By abstracting out common patterns into reusable functions, you can write cleaner and more maintainable code.

#### Common Higher-Order Functions π

Let's explore some of the most commonly used higher-order functions in JavaScript:

1. `map` πΊοΈ
2. `filter` π
3. `reduce` β
##### 1. `map` πΊοΈ

The `map` function creates a new array by applying a given function to each element of the original array.

``````const numbers = [1, 2, 3, 4, 5];
const doubled = numbers.map(num => num * 2);

console.log(doubled); // [2, 4, 6, 8, 10]
``````

In this example, `map` takes a function that doubles each number and applies it to every element in the `numbers` array.

##### 2. `filter` π

The `filter` function creates a new array containing all the elements that pass a test implemented by a given function.

``````const numbers = [1, 2, 3, 4, 5];
const evenNumbers = numbers.filter(num => num % 2 === 0);

console.log(evenNumbers); // [2, 4]
``````

Here, `filter` takes a function that checks if a number is even and applies it to each element, returning only the even numbers.

##### 3. `reduce` β

The `reduce` function applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.

``````const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((accumulator, currentValue) => accumulator + currentValue, 0);

console.log(sum); // 15
``````

In this case, `reduce` sums up all the numbers in the array, starting from an initial value of 0.

#### Custom Higher-Order Functions π οΈ

You can also create your own higher-order functions. Let's create a simple `repeat` function that repeats a given action a specified number of times.

``````function repeat(action, times) {
for (let i = 0; i < times; i++) {
action(i);
}
}

repeat(console.log, 5);
// Output:
// 0
// 1
// 2
// 3
// 4
``````

In this example, `repeat` takes a function (`action`) and a number (`times`), then calls the function the specified number of times.

#### Combining Higher-Order Functions π

Higher-order functions can be combined to perform complex operations in a clean and readable way. For instance, let's filter even numbers from an array, double them, and then sum them up.

``````const numbers = [1, 2, 3, 4, 5];

const result = numbers
.filter(num => num % 2 === 0)
.map(num => num * 2)
.reduce((acc, num) => acc + num, 0);

console.log(result); // 12 (2*2 + 4*2)
``````

Here, we first filter out the even numbers, then double each of them, and finally sum them up.

### Conclusion π

Higher-order functions are a cornerstone of functional programming in JavaScript. They allow you to write more declarative and modular code by abstracting common patterns into reusable functions. By mastering `map`, `filter`, `reduce`, and creating your own higher-order functions, you can significantly improve your coding skills and productivity.

Happy coding! π»β¨