# Introduction to the Recursion Pattern in JavaScript

Tram Ho

In programming, recursion is when a function calls itself. This can be useful for solving problems that can be divided into smaller, similar problems. The process of breaking down a problem into smaller pieces is called “divide and conquer.”

Functional programming is a programming paradigm (a way of organizing code) that emphasizes the use of functions. In functional programming, it is common to use recursion to solve problems.

# Examples

Here are five examples of real-world problems that can be solved using the recursion pattern in JavaScript with functional-oriented programming:

## Calculating the Factorial of a Number

The factorial of a number is the product of all the numbers from 1 to that number. For example, the factorial of 5 (written as 5!) is 1 * 2 * 3 * 4 * 5 = 120. Here is a recursive function that calculates the factorial of a number:

## Flattening an Array

Sometimes, you may have an array that contains other arrays as elements. You can use recursion to flatten the array and return a new array with all the elements in a single level. Here is a recursive function that flattens an array:

## Finding an Element in an Array

You can use recursion to search for an element in an array. Here is a recursive function that searches for an element in an array and returns its index if found, or -1 if not found:

## Reversing a String

You can use recursion to reverse a string by breaking it down into smaller strings and concatenating them in the opposite order. Here is a recursive function that reverses a string:

## Generating the Fibonacci Sequence

The Fibonacci sequence is a series of numbers in which each number is the sum of the two preceding ones, usually starting with 0 and 1. You can use recursion to generate the Fibonacci sequence. Here is a recursive function that generates the Fibonacci sequence:

# Conclusion

The recursion pattern is a powerful technique for solving problems in JavaScript with functional-oriented programming. It allows you to break down a problem into smaller, similar problems and solve them recursively. In this article, we looked at five examples of real-world problems that can be solved using the recursion pattern. By understanding and mastering the recursion pattern, you can become a more effective and efficient programmer.

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