in Dataset/JS/AngularCalendar/calendar.js [127:140]
var subtractAsSets = function (a, b) {
var obj = (b || []).reduce(
function (rslt, val) {
rslt[val] = true;
return rslt;
},
Object.create(null)
);
return (a || []).filter(
function (val) {
return !obj[val];
}
);
};