remove-decimals-refactor.js

function removeDecimalNumbers([ head, ...tail ]) {
  if (!head) return []

  return Number.isInteger(head)
    ? [head, ...removeDecimalNumbers(tail)]
    : removeDecimalNumbers(tail)
}

module.exports = {
  removeDecimalNumbers
}

without-refactor.js

function removeDecimalNumbers(numberArr) {
  if (numberArr.length <= 0) {
    return []
  }

  let firstElement = numberArr[0]
  let restElements = numberArr.slice(1, numberArr.length)

  const withoutDecimals = removeDecimalNumbers(restElements)

  if (Number.isInteger(firstElement)) {
    return [firstElement].concat(withoutDecimals)
  } else {
    return withoutDecimals
  }
}

module.exports = {
  removeDecimalNumbers
}