JavaScript sum of a number

Question

I have this number 55555

If we add this single number then the result will be = 25 and then if we add 2 + 5 then the result will be 7.

I want to make it but can't get the result:

What I have done so far:

function createCheckDigit(membershipId) {
  // Write the code that goes here.
    string = membershipId.split('');                
    let sum = 0;                               
    for (var i = 0; i < string.length; i++) {  
        sum += parseInt(string[i],10);         
    }
  
    console.log(sum.split(''));
   
    
  
}

console.log(createCheckDigit("55555"));

Answer 1

Make the function recursive - after the loop, if the sum is 10 or more, call it again:

function createCheckDigit(membershipId) {
  // Write the code that goes here.
    string = membershipId.split('');                
    let sum = 0;                               
    for (var i = 0; i < string.length; i++) {  
        sum += parseInt(string[i],10);         
    }
    return sum >= 10 ? createCheckDigit(String(sum)) : sum;
}

console.log(createCheckDigit("55555"));

Or, more concisely:

function createCheckDigit(num) {
  const nextNum = num.split('').reduce((a, b) => a + Number(b), 0);
  return nextNum >= 10 ? createCheckDigit(String(nextNum)) : nextNum;
}

console.log(createCheckDigit("55555"));

Answer 2

function makesum(value)
{
    return value.toString().split('').reduce((a,b) => a/1+b/1);              
    
}
function actualFunction(newvalue)
{
    if(newvalue.toString().split('').length < 2)
    {
   return makesum(newvalue);
    }
    else
    {
           return makesum(makesum(newvalue));
    }
}

console.log(actualFunction(55555))
console.log(actualFunction(1111111111))
console.log(actualFunction(99))