Function isDate

codebase/sources/dhtmlxscheduler.js:15803–15805

(value)

    return year % 4 === 0 && year % 100 !== 0 || year % 400 === 0;
  };
  var isDate = function(value) {
    return value instanceof Date;
  };
  var isValidDate = function(value) {
    return isDate(value) && !isNaN(value.getTime());
  };