Sum of digits using Recursion in Javascript.

function sumOfDigits(n){

    let num = parseInt(n/10); 
    let digit = n%10; 
    if(n ==0){
        return n;
    }
 
   return digit + sumOfDigits(num);
    
}

let sum= sumOfDigits(99999);
console.log("result"  + sum);

9 + sumOfDigits(9999) = returns 9 + 36  = 45

     9 + sumOfDigits(999) = returns 9 + 27  = 36

             9 + sumOfDigits(99)  = returns 9 + 18  = 27

                    9 + sumOfDigits(9)  = returns 9 + 9 = 18

                        9 + sumOfDigits(0)  = returns 9

So finally it returns 45, which is the sum of digits.