A function to call focus() on the first form input that has an error

focusOnFirstError.js

function focusOnFirstError(formName, hasError) {
  const form = document.forms[formName]
  for (let i = 0; i < form.length; i++) {
    if (hasError(form[i].name)) {
      form[i].focus()
      break
    }
  }
}