Function isDate

codebase/sources/dhtmlxscheduler.es.js:15799–15801

(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());
};