code.gs

const COLLECTION_URL = 'https://boardgamegeek.com/xmlapi2/collection?username=grapswiz';
const THING_URL = 'https://boardgamegeek.com/xmlapi2/thing';

function myFunction() {
  const collectionResponse = UrlFetchApp.fetch(COLLECTION_URL);
  const xmlDocs = XmlService.parse(collectionResponse.getContentText());
  const items = xmlDocs.getRootElement().getChildren('item');
  const ids = items.map((item) => item.getAttribute('objectid').getValue());
  Logger.log(ids.length);

  const sliced = sliceByNumber(ids, 100);
  const thingResponse = UrlFetchApp.fetch(`${THING_URL}?id=${sliced[0].join(',')}`);
  const xmlDocsForThing = XmlService.parse(thingResponse.getContentText());
  const thingItems = xmlDocsForThing.getRootElement().getChildren('item');
  const output = thingItems.map(ti => {
    const link = ti.getChildren('link');
    const categories = [];
    const mechanics = [];
    const designers = [];
    const artists = [];
    const publishers = [];
    for (const l of link) {
      const type = l.getAttribute('type').getValue();
      const value = l.getAttribute('value').getValue();
      if (type === 'boardgamecategory') {
        categories.push(value);
      } else if (type === 'boardgamemechanic') {
        mechanics.push(value);
      } else if (type === 'boardgamedesigner') {
        designers.push(value);
      } else if (type === 'boardgameartist') {
        artists.push(value);
      } else if (type === 'boardgamepublisher') {
        publishers.push(value);
      }
    }

    return {
      id: ti.getAttribute('id').getValue(),
      name: ti.getChild('name').getAttribute('value').getValue(),
      thumbnail: ti.getChild('thumbnail').getValue(),
      minplayers: ti.getChild('minplayers').getAttribute('value').getValue(),
      maxplayers: ti.getChild('maxplayers').getAttribute('value').getValue(),
      playingtime: ti.getChild('playingtime').getAttribute('value').getValue(),
      yearpublished: ti.getChild('yearpublished').getAttribute('value').getValue(),
      categories: categories,
      mechanics: mechanics,
      designers: designers,
      artists: artists,
      publishers: publishers
    };
  });
  Logger.log(output);
}

const sliceByNumber = (array, number) => {
  const length = Math.ceil(array.length / number)
  return new Array(length).fill().map((_, i) =>
    array.slice(i * number, (i + 1) * number)
  )
};