in book/master_middleman/source/javascripts/waypoints/context.js [46:53]
Context.prototype.checkEmpty = function() {
var horizontalEmpty = this.Adapter.isEmptyObject(this.waypoints.horizontal)
var verticalEmpty = this.Adapter.isEmptyObject(this.waypoints.vertical)
if (horizontalEmpty && verticalEmpty) {
this.adapter.off('.waypoints')
delete contexts[this.key]
}
}