C PART

TEST#1 JAVASCRIPT

function sumStrings(a,b) {
  let result = 0;
  a.split("").reverse().forEach((element, index) => {
    result += parseInt(element,10) * Math.pow(10, index);
  })
  
  b.split("").reverse().forEach((element, index) => {
    result += parseInt(element,10) * Math.pow(10, index);
  })
  
  return result.toString();
}

TEST#2 JAVASCRIPT [SOLUTION]

function sumStrings(a,b) {
  return ((BigInt(a) + BigInt(b))).toString();
}