discourse/app/assets/javascripts/discourse/views/poster-expansion.js.es6

var clickOutsideEventName = "mousedown.outside-poster-expansion";

export default Discourse.View.extend({
  elementId: 'poster-expansion',
  classNameBindings: ['controller.visible::hidden', 'controller.showBadges'],

  _setup: function() {
    var self = this;
    this.appEvents.on('poster:expand', function(target) {
      if (!target) { return; }
      Em.run.schedule('afterRender', function() {
        if (target) {
          var position = target.offset();
          if (position) {
            position.left += target.width() + 5;
            self.$().css(position);
          }
        }
      });
    });

    $('html').off(clickOutsideEventName).on(clickOutsideEventName, function(e) {
      if (self.get('controller.visible')) {
        var $target = $(e.target);
        if ($target.closest('.trigger-expansion').length > 0) { return; }
        if (self.$().has(e.target).length !== 0) { return; }

        self.get('controller').close();
      }

      return true;
    });
  }.on('didInsertElement'),

  _removeEvents: function() {
    $('html').off(clickOutsideEventName);
    this.appEvents.off('poster:expand');
  }.on('willDestroyElement')

});