addMethod.js

gistfile1.txt

function addNumber (...arg) {
  let calculator = 0;
  if(arg.length === 0){
    throw new Error('The input cannot be empty');
  }
  for (let index = 0; index < arg.length; index++) {
    if(typeof arg[index] !== 'number'){
      return 'Input must be a number';
    } 
    calculator += arg[index];
  }
  return calculator;
}

module.exports = addNumber;