validation-rules.js

const getValidationRules = (el) => {
  const rules = [];
  const required = el.hasAttribute('required')
  const min = el.getAttribute('min')
  const max = el.getAttribute('max')
  const maxlength = el.getAttribute('maxlength')
  const minlength = el.getAttribute('minlength')
  const pattern = el.getAttribute('pattern')

  if (required) {
    rules.push(val => val.length > 0)
  }

  if (min !== null) {
    rules.push(val => val >= min)
  }

  if (max !== null) {
    rules.push(val => val <= max)
  }

  if (minlength !== null) {
    rules.push(val => val.length >= minlength)
  }

  if (maxlength !== null) {
    rules.push(val => val.length <= maxlength)
  }

  if (pattern !== null) {
    rules.push(val => val.match(new RegExp(pattern)))
  }

  return rules
}