inject.js

function injectPage(url) {

  var CONTAINER_SELECTOR = '.content';
  
  //Show loading indicator
  document.querySelector(CONTAINER_SELECTOR).innerHTML = '<center>Loading...</center>';

  url = decodeURI(url);

  var xhr = new XMLHttpRequest();
  xhr.open('GET', url);
  xhr.responseType = 'document';
  xhr.overrideMimeType("text/html; charset=utf-8");
  xhr.onloadend = function(e) {

    if (e.target.status != 200) {
      // error handling
      return;
    }

    var injectDoc = e.target.response;

    var meta = injectDoc.head.querySelector('meta[itemprop="name"]');
    if (meta) {
      var metaContentName = injectDoc.head.querySelector('meta[itemprop="name"]').content;
      document.head.querySelector('meta[itemprop="name"]').content = metaContentName;
    }

    // Inject article body.
    var container = document.querySelector(CONTAINER_SELECTOR);
    var newDocContainer = injectDoc.querySelector(CONTAINER_SELECTOR);
    $(container).html(newDocContainer.innerHTML);

    // Scroll to top of page
    window.scrollTo(0, 0);
  };

  xhr.send();
}