Collect all errors of an html form. The "errors" object can be serialized.

collect-html-form-errors.js

/**
 * Considering that each html input
 * has a "name" attribute and proper
 * validation attributes (type, pattern, required, etc)
 * we collect "validity" states of invalid inputs
 * and the "validationMessage" provided by the browsers
 */
const errors = Array.from(form.elements)
  .filter((el) => el.hasAttribute('name'))
  .reduce((acc, el) => {
    const field = el.validity ? el : el[0];
    if (!field.validity.valid) {
      acc[field.name] = {
        validity: field.validity,
        validationMessage: field.validationMessage
      };
    }
    return acc;
  }, {});