go-back-with-backspace/content_script.js

// Copyright 2016 Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Load the options, then register a keyboard listener.  We capture the event
// at the Window to let any handlers or listeners registered on the Document
// have a chance to handle it first.
var options;
chrome.storage.sync.get({
  blacklist: [],
  disableInApplets: true,
  whitelist: []
}, function(items) {
  options = items;
  window.addEventListener('keydown', function(e) {
    handleBackspace(e);
  });
});

// Update the local options when they're changed externally.
chrome.storage.onChanged.addListener(function(changes, area) {
  if (area === 'sync') {
    if (changes.blacklist)
      options.blacklist = changes.blacklist.newValue;
    if (changes.disableInApplets)
      options.disableInApplets = changes.disableInApplets.newValue;
    if (changes.whitelist)
      options.whitelist = changes.whitelist.newValue;
  }
});

// Check for shift-backspace or unmodified backspace and navigate if
// applicable.
function handleBackspace(e) {
  if (e.defaultPrevented ||
      e.key !== 'Backspace' ||
      e.altKey ||
      e.ctrlKey ||
      e.metaKey)
    return;

  // The blacklist overrides everything.
  var url = window.location.href;
  if (options.blacklist.includes(url))
    return;

  // The whitelist overrides applet focus.
  // Listening on the Window means the event has no path (see
  // http://crbug.com/645527), so we'll have to look at the focused (active)
  // element. This means it will not work properly with shadow DOM.
  // TODO: Fix behavior with shadow DOM when the above bug is resolved.
  if (!options.whitelist.includes(url) &&
      disabledInApplet(document.activeElement))
    return;
  if (isEditable(document.activeElement))
    return;

  e.shiftKey ? window.history.forward(): window.history.back();
  e.preventDefault();
}

// Return true if the option to disable the extension in applets is enabled,
// and focus is in an embedded Flash or Java applet.
function disabledInApplet(target) {
  if (!options.disableInApplets)
    return false;

  var nodeName = target.nodeName.toUpperCase();
  var nodeType = target.type || '';
  nodeType = nodeType.toLowerCase();
  if ((nodeName === 'EMBED' || nodeName === 'OBJECT') &&
      (nodeType === 'application/x-shockwave-flash' ||
       nodeType === 'application/java')) {
    return true;
  }
  return false;
}