@shko.online/dataverse-odata/lib/esm/getFetchXmlFromParser.js

This package will help parse OData strings (only the Microsoft Dataverse subset). It can be used as a validator, or you can build some javascript library which consumes the output of this library.

import { atMostOnce } from './validators/atMostOnce';
import { differentFromEmptyString } from './validators/differentFromEmptyString';
const option = 'fetchXml';

/**
 * Parses the {@link ODataFetch.fetchXml fetchXml} query
 * @returns Returns `false` when the parse has an error
 */
export const getFetchXmlFromParser = (parser, result) => {
  const value = parser.getAll(option);
  if (value.length === 0) {
    return true;
  }
  if (!atMostOnce(option, value, result) || !differentFromEmptyString(value, result)) {
    return false;
  }
  const fetchXml = value[0];
  const serializer = new DOMParser();
  const fetchXmlDocument = serializer.parseFromString(fetchXml, 'text/xml');
  if (fetchXmlDocument.documentElement.tagName === 'parsererror') {
    result.error = {
      code: '0x80040201',
      message: 'Invalid XML.'
    };
    return false;
  }
  const entity = fetchXmlDocument.evaluate('fetch/entity', fetchXmlDocument, null, XPathResult.ANY_TYPE, null).iterateNext();
  if (fetchXmlDocument.documentElement.children.length != 1 || !entity || !entity.getAttribute('name')) {
    result.error = {
      code: '0x80041102',
      message: 'Entity Name was not specified in FetchXml String.'
    };
    return false;
  }
  const invalidAttribute = fetchXmlDocument.evaluate('fetch/entity/*[not(self::filter or self::order or self::link-entity or self::attribute or self::all-attributes or self::no-attrs)]', fetchXmlDocument, null, XPathResult.ANY_TYPE, null).iterateNext();
  if (invalidAttribute) {
    result.error = {
      code: '0x8004111c',
      message: `Invalid Child Node, valid nodes are filter, order, link-entity, attribute, all-attributes, no-attrs. NodeName = ${invalidAttribute.tagName} NodeXml = ${invalidAttribute.outerHTML}`
    };
    return false;
  }
  result.fetchXml = fetchXmlDocument;
  return true;
};