Backbone VisEventsView

gistfile1.js

var VisEventsView = Backbone.View.extend({
  // A Backbone.View extension that allows a View to trigger events when
  // it's visibility changes. The view may also listen to its own visibility
  // events.

  setup_visibility_observer: function() {
    // Check if view element is visible when attributes of el change.
    var t = this;
    _.bindAll(t, 'check_visibility');
    t.visibility_observer = new MutationObserver(t.check_visibility);
    t.visibility_observer.observe(t.el, {attributes: true});
  },

  setup_dom_insertion_observer: function() {
    // Check if view element is visible when DOM elements are
    // inserted or removed.
    var t = this;
    _.bindAll(t, 'check_visibility');
    t.insertion_observer = new MutationObserver(t.check_visibility);
    t.insertion_observer.observe(document, {childList: true, subtree: true});
  },

  check_visibility: function() {
    var t = this;
    var visible = t.$el.is(":visible");
    if (visible) {

      // If currently visible, and hidden as of last mutation,
      // fire `visible` event and set visibility to true.
      if (t.visibility !== true) {
        t.visibility = true;
        t.trigger('visible');
      }

    } else {
      // If currently not visible, and visible as of last mutation,
      // fire `hidden` event and set visibility to false.
      if (t.visibility !== false) {
        t.visibility = false;
        t.trigger('hidden');
      }
    }
   },

});

Not recommended for performance reasons in apps with lots of DOM mutation. It should be possible to improve performance by defining the MutationObserver to be more specific, rather than listening to document and it's subtree.