go-back-with-backspace/content_script.js

// Listen for shift-backspace or unmodified backspace and navigate if not in
// an editable field. We capture the event at the Window to let any handlers
// or listeners registered on the Document have a chance to handle it first.
window.addEventListener('keydown', function(e) {
  // 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 (e.key === 'Backspace' &&
      !e.defaultPrevented &&
      !e.altKey &&
      !e.ctrlKey &&
      !e.metaKey &&
      !isEditable(document.activeElement)) {
    e.shiftKey ? window.history.forward(): window.history.back();
    e.preventDefault();
  }
});