Recursion is a programming technique that allows a function to call itself repeatedly until a certain condition is met. Recursion is an essential concept in computer science and is widely used in programming languages such as JavaScript.

In this article, we will understand about recursion in JavaScript in detail. We will discuss the basics of recursion, recursive functions, and the differences between recursive and iterative functions. We will also provide some best practices for writing efficient and error-free recursive functions.

## Table of Contents

- Basics of Recursion in JavaScript
- Understanding Recursion: How it works
- Terminating a Recursive Function
- Base Case and Recursive Case

- Recursive Functions
- Factorial Function
- Fibonacci Sequence
- Sum of Digits Function

- Recursive vs. Iterative Functions
- Best Practices for Recursion in JavaScript
- Conclusion

## 1. Basics of Recursion in JavaScript

Let’s understand some of the basics of recursions in javascript.

### Understanding Recursion: How it works

When a function calls itself, it creates a new instance of itself with its own set of local variables. The new instance of the function then executes the same code as the original function, and may also call itself again. This process continues until a base case is reached, at which point the function stops calling itself and the instances are destroyed.

### Terminating a Recursive Function

One of the most important things to consider when writing a recursive function is the termination condition. Without a proper termination condition, the function will continue to call itself indefinitely, causing an infinite loop and crashing the program. It is crucial to ensure that the termination condition is set up correctly to avoid this issue.

### Base Case and Recursive Case

The base case is the condition that determines when the recursion should stop. It is the simplest form of the problem that can be solved directly. The recursive case is the condition that determines when the function should call itself again. It is important to have both a base case and a recursive case in order to properly implement recursion.

## 2. Recursive Functions

There are many examples of recursive functions in JavaScript. Let's look at a few of the most common ones.

### Factorial Function

The factorial of a number is the product of all the integers from 1 to that number. For example, the factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120.

```
function factorial(n) {
if (n === 1) {
return 1;
}
return n * factorial(n - 1);
}
```

In the above function, the base case is when n is equal to 1, and the recursive case is when n is greater than 1. The function calls itself with n - 1 until the base case is reached.

### Fibonacci Sequence

The Fibonacci sequence is a series of numbers in which each number is the sum of the two preceding numbers. The sequence starts with 0 and 1, and the next number in the sequence is the sum of the previous two numbers. For example, the first ten numbers in the Fibonacci sequence are: 0, 1, 1, 2, 3, 5, 8, 13.

```
function fibonacci(n) {
if (n === 0) {
return 0;
}
if (n === 1) {
return 1;
}
return fibonacci(n - 1) + fibonacci(n - 2);
}
```

In the above function, the base cases are when n is equal to 0 or 1, and the recursive case is when n is greater than 1. The function calls itself with n - 1 and n - 2 until the base case is reached.

### Sum of Digits Function

The sum of digits function calculates the sum of the digits of a given number. For example, the sum of digits of the number 123 is 1 + 2 + 3 = 6.

```
function sumOfDigits(n) {
if (n < 10) {
return n;
}
return (n % 10) + sumOfDigits(Math.floor(n / 10));
}
```

In the above function, the base case is when n is less than 10, and the recursive case is when n is greater than or equal to 10. The function calls itself with Math.floor(n / 10) to remove the last digit of the number and adds that digit to the result.

## 3. Recursive vs. Iterative Functions

Recursive and iterative functions can be used to solve the same problem, but they differ in their implementation. Recursive functions call themselves, while iterative functions use loops to repeat a set of instructions. Recursive functions can be easier to understand and write for certain problems, but they can also be less efficient and have a higher risk of causing an infinite loop.

## 4. Best Practices for Recursion in JavaScript

To write efficient and error-free recursive functions in JavaScript, here are some best practices to follow:

- Set up the termination condition properly to avoid infinite loops.
- Use tail recursion whenever possible to improve performance.
- Use memoization to cache the results of previously computed values.
- Avoid using recursion for problems that can be solved iteratively.
- Test your recursive functions thoroughly to ensure correctness and performance.

## 5. Conclusion

In this article, we came to know about recursion in JavaScript in detail. We have discussed the basics of recursion, recursive functions, and the differences between recursive and iterative functions. We have also provided some best practices for writing efficient and error-free recursive functions.

Recursion is a powerful programming technique that can be used to solve many complex problems in a simple and elegant way. However, it is important to understand the basics of recursion and to follow best practices when implementing it to avoid common pitfalls.