let outlines = sites.filter((site) => !!site.rss).map((site) => {
  return `<outline type="rss" xmlUrl="${site.rss}" title="${site.title}"/>`;
});

let template = `<?xml version="1.0" encoding="UTF-8"?><opml version="1.1"><head></head><body>${outlines.join("")}</body></opml>`;

window.onload = function(){
  let a = document.getElementById("opml");
  a.setAttribute("href", "data:text/plain;charset=utf-8," + window.encodeURIComponent(template));
  a.setAttribute("download", "webring.opml");
}