Function to add up all the natural numbers from 1 to num in JavaScript

We are required to write a JavaScript function that takes in a number, say num.

Then our function should return the sum of all the natural numbers between 1 and num, including 1 and num.

For example, if num is −

const num = 5;

Then the output should be −

const output = 15;

because,

1+2+3+4+5 = 15

We will use the below formula to solve this problem −

Sum of all natural number upto n =

((n*(n+1))/2)

Example

The code for this will be −

const num = 5;
const sumUpto = num => {
   const res = (num * (num + 1)) / 2;
   return res;
};
console.log(sumUpto(num));
console.log(sumUpto(7));
console.log(sumUpto(45));
console.log(sumUpto(2));
console.log(sumUpto(8));
console.log(sumUpto(99));

Output

And the output in the console will be −

15
28
1035
3
36
4950