ThinkAmI uses the XMLService of Google Apps Script to create a valid RSS feed that is served to the browser using ContentService with the MIME type set as RSS. Should be handy for creating RSS feeds for services like the Google Search Scraper that do not natively offer feeds.

/* Credit: https://gist.github.com/thinkAmi */

function doGet() {
  var rss = makeRss();

  rss.setTitle('RSS 2.0 Feed with Google Apps Script');
  rss.setLink('http://example.com');
  rss.setDescription('RSS 2.0 Feed');
  rss.setLanguage('en');
  rss.setAtomlink('http://example.com/rss');

  for (var i = 1; i < 3; i++) {
    rss.addItem({
      title: 'TITLE:' + i,
      link: 'http://example.com/#' + i,
      description: 'DESCRIPTION: ' + i,
      pubDate: new Date(),
    });
  }

  return ContentService.createTextOutput(rss.toString()).setMimeType(ContentService.MimeType.RSS);
}

var makeRss = function () {
  var channel = XmlService.createElement('channel');
  var root = XmlService.createElement('rss')
    .setAttribute('version', '2.0')
    .setAttribute('xmlnsatom', 'http://www.w3.org/2005/Atom')
    .addContent(channel);

  var title = '';
  var link = '';
  var description = '';
  var language = '';
  var atomlink = '';
  var items = {};

  var createElement = function (element, text) {
    return XmlService.createElement(element).setText(text);
  };

  return {
    setTitle: function (value) {
      title = value;
    },
    setLink: function (value) {
      link = value;
    },
    setDescription: function (value) {
      description = value;
    },
    setLanguage: function (value) {
      language = value;
    },
    setAtomlink: function (value) {
      atomlink = value;
    },

    addItem: function (args) {
      if (typeof args.title === 'undefined') {
        args.title = '';
      }
      if (typeof args.link === 'undefined') {
        args.link = '';
      }
      if (typeof args.description === 'undefined') {
        args.description = '';
      }
      if (!(args.pubDate instanceof Date)) {
        throw 'pubDate Missing';
      }
      if (typeof args.timezone === 'undefined') {
        args.timezone = 'GMT';
      }
      if (typeof args.guid === 'undefined' && typeof args.link === 'undefined') {
        throw 'GUID ERROR';
      }

      var item = {
        title: args.title,
        link: args.link,
        description: args.description,
        pubDate: Utilities.formatDate(args.pubDate, args.timezone, 'EEE, dd MMM yyyy HH:mm:ss Z'),
        guid: args.guid === 'undefined' ? args.link : args.link,
      };

      items[item.guid] = item;
    },

    toString: function () {
      channel.addContent(
        XmlService.createElement('atomlink')
          .setAttribute('href', atomlink)
          .setAttribute('rel', 'self')
          .setAttribute('type', 'application/rss+xml')
      );

      channel.addContent(createElement('title', title));
      channel.addContent(createElement('link', link));
      channel.addContent(createElement('description', description));
      channel.addContent(createElement('language', language));

      for (var i in items) {
        channel.addContent(
          XmlService.createElement('item')
            .addContent(createElement('title', items[i].title))
            .addContent(createElement('link', items[i].link))
            .addContent(createElement('description', items[i].description))
            .addContent(createElement('pubDate', items[i].pubDate))
            .addContent(createElement('guid', items[i].guid))
        );
      }

      var document = XmlService.createDocument(root);
      var xml = XmlService.getPrettyFormat().format(document);

      var result = xml.replace('xmlnsatom', 'xmlns:atom').replace('<atomlink href=', '<atom:link href=');

      return result;
    },
  };
};