JavaScript Program to Find Sum of Natural Numbers Using Recursion

In this example, you will learn to write a JavaScript program that finds the sum of natural numbers using recursion.

To understand this example, you should have the knowledge of the following JavaScript programming topics:


The positive integers 1, 2, 3, ... are known as natural numbers.

Example: Sum of Natural Numbers Using Recursion

// program to find the sum of natural numbers using recursion

function sum(num) {
    if(num > 0) {
        return num + sum(num - 1);
    }
    else {
        return num;
    }
 }

// take input from the user
const number = parseInt(prompt('Enter a positive integer: '));

const result = sum(number);

// display the result
console.log(`The sum is ${result}`);

Output

Enter a positive integer: 5
The sum is 15

In the above program, the user is prompted to enter a number.

Then the sum() function is called by passing the parameter (here 5) that the user entered.

  • If the number is greater than 0, the function calls itself by decreasing the number by 1.
  • This process continues until the number is 1. When the number reaches 0, the program stops.
  • If the user enters a negative number, the negative number is returned and the program stops.

Here,

sum(5) returns 5 + sum(4)
sum(4) returns 5 + 4 + sum(3)
sum(3) returns 5 + 4 + 3 + sum(2)
sum(2) returns 5 + 4 + 3 + 2 + sum(1)
sum(1) returns 5 + 4 + 3 + 2 + 1 + sum(0)
sum(0) returns 5 + 4 + 3 + 2 + 1 + 0