Mathematics summation function in JavaScript

Problem

We are required to write a JavaScript function that takes in a number n. Our function should return the sum of all the natural numbers from 1 to n including both 1 and n.

Example

Following is the code ?

const num = 34;
const summation = (num = 1) => {
    let res = 0;
    for(let i = 1; i <= num; i++){
        res += i;
    };
    return res;
};
console.log(summation(num));

Output

Following is the console output ?

595

Using Mathematical Formula (Optimized)

Instead of using a loop, we can use the mathematical formula for the sum of first n natural numbers: n × (n + 1) / 2

const summationFormula = (num) => {
    return (num * (num + 1)) / 2;
};

console.log(summationFormula(34));  // Same result
console.log(summationFormula(100)); // Testing with larger number

595
5050

Comparison

Conclusion

Both methods calculate the sum of natural numbers effectively. The mathematical formula approach is more efficient with O(1) time complexity, while the loop method is easier to understand for beginners.