Function isValidDate

codebase/sources/dhtmlxscheduler.js:15806–15808

(value)

    return value instanceof Date;
  };
  var isValidDate = function(value) {
    return isDate(value) && !isNaN(value.getTime());
  };
  var daysBetween = function(date1, date2) {
    var date1ms = date1.getTime();
    var date2ms = date2.getTime();