in Hands-on lab/lab-files/src/Contoso Sports League/Contoso.Apps.SportsLeague.Web/wwwroot/js/plugins.js [352:382]
Dropdown.prototype.keydown = function (e) {
if (!/(38|40|27|32)/.test(e.which) || /input|textarea/i.test(e.target.tagName)) return
var $this = $(this)
e.preventDefault()
e.stopPropagation()
if ($this.is('.disabled, :disabled')) return
var $parent = getParent($this)
var isActive = $parent.hasClass('open')
if (!isActive && e.which != 27 || isActive && e.which == 27) {
if (e.which == 27) $parent.find(toggle).trigger('focus')
return $this.trigger('click')
}
var desc = ' li:not(.disabled):visible a'
var $items = $parent.find('.dropdown-menu' + desc)
if (!$items.length) return
var index = $items.index(e.target)
if (e.which == 38 && index > 0) index-- // up
if (e.which == 40 && index < $items.length - 1) index++ // down
if (!~index) index = 0
$items.eq(index).trigger('focus')
}