@anandabastakoti/sum-of-digits/index.js

This is the firs npm package I developed in which the function takes an positive integer and returns the sum of all the digits

function sumOfDigits(input) {
  if (typeof input === "string") return "Only number inputs are allowed!";
  if (typeof input === "boolean") return "Only number inputs are allowed!";
  if (typeof input !== "number" || input < 0)
    return "Input must be a positive number!";

  return input
    .toString()
    .split("")
    .map(Number)
    .reduce((a, b) => a + b, 0);
}

module.exports = sumOfDigits;