Show RSS feeds on a Web page via pure JavaScript, incl. code to bypass Chrome's CORS policy.

.htaccess

# enable CORS policy
# https://gist.github.com/maxparm/3105526
<IfModule mod_rewrite.c>
  Header add Access-Control-Allow-Origin "*"
  Header add Access-Control-Allow-Methods: "GET,POST,OPTIONS,DELETE,PUT"
  Header add Access-Control-Allow-Headers: "Content-Type"

  RewriteEngine on
  RewriteBase /
</IfModule>

example-calls.html

<script type="text/javascript">
  document.write('<h4>Blog posts at <a href="/r">R / Notes</a> (in English)</h4>');
  document.write('<div class="feed"><ul id="r"></ul></div>');
  parse('https://f.briatte.org/r/rss', 'r');

  document.write('<h4>Blog posts at <a rel="external" href="https://politbistro.hypotheses.org/">Polit&rsquo;&nbsp;bistro</a> (in French)</h4>');
  document.write('<div class="feed"><ul id="politbistro"></ul></div>');
  parse('https://politbistro.hypotheses.org/feed', 'politbistro');
</script>

parse.js

// based on https://github.com/pokiiio/hatena-blog-parser
function parse(rssUrl, rssList) {
    const request = new XMLHttpRequest();
    request.open('GET', rssUrl);
    request.addEventListener('load', (event) => {
      if (event.target.status !== 200) {
        const e = '<p>Error ' + event.target.status + ': ' + event.target.statusText + ' (sorry)</p>';
          document.getElementById(rssList).insertAdjacentHTML('beforeend', e);
          return;
      }

      const result = event.target.responseText;

      let data = [];

      result.split('<item>').forEach(element => {
        const postTitle = element.split('<title>')[1].split('</title>')[0];
        const postLink = element.split('<link>')[1].split('</link>')[0];

        var postDate = undefined; // item 0 (blog link/title) has no pubDate
        if (element.includes('<pubDate>')) {
          var postDate = element.split('<pubDate>')[1].split('</pubDate>')[0];
        };

        let post = {};
        post.postTitle = postTitle;
        post.postLink = postLink;
        post.postDate = postDate;
        data.push(post);
      });

      var d = document.getElementById(rssList);
      var i;
      for (i = 1; i < 4; i++) {
        var t = data[i].postDate; // MMM DD, YYYY
        var t = '<div class="date">' + t.substring(8, 11) + ' ' + t.substring(5, 7) + ', ' + t.substring(12, 16) + '</div>';
        var s = '<li>' + t + '<a target="_blank" href="' + data[i].postLink + '">' + data[i].postTitle + '</a></li>';
        d.insertAdjacentHTML('beforeend', s);
      }
    });
    request.send();
}

style.css

.feed ul {
  width: 95%;
  list-style: none;
  margin: 0;
  color: #3E3E3E;
}
.feed li {
  padding: 1em 0;
  clear: both;
}
.feed .date {
  font-family: "Inconsolata", monospace;
  float: left;
  line-height: 150%;
  width: 17%;
  color: #999;
  margin-right: 1em;
}
.feed a {
  line-height: 150%;
  width: 80%;
  float: right;
}