const getSeries = function(series, groupSize) {
  // checking if the values provided match the description
  if (series == null) return 'provide a string';
  if (groupSize == null) return 'provide size';
  if (Number.isInteger(groupSize) == false)
    return 'provide a whole number for size';
  if (groupSize == 0) return 'size cannot be 0';

  // creating arrays
  const arrayOfNumbers = [];
  const arrayOfNumericArrays = [];

  // spliting the string provided into groups
  const arrayOfStrings = series.match(new RegExp('.{' + groupSize + '}', 'g'));
  arrayOfStrings.forEach(element => {
    arrayOfNumbers.push(parseInt(element));
  });

  // checking if there is a part of the string thats left ungrouped
  if ((series.length / groupSize) % 1 != 0)
    arrayOfNumbers.push(parseInt(series.slice(-groupSize)));

  // transforming the result into the desired format
  arrayOfNumbers.forEach(element => {
    const digits = element.toString().split('');
    const realDigits = digits.map(Number);
    arrayOfNumericArrays.push(realDigits);
  });

  return arrayOfNumericArrays;
};