function isLeapYear(year) {
  //>>includeStart('debug', pragmas.debug);
  if (year === null || isNaN(year)) {
    throw new DeveloperError("year is required and must be a number.");
  }
  //>>includeEnd('debug');

  return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
}
Determines if a given date is a leap year.

@function isLeapYear

@param {number} year The year to be tested.
@returns {boolean} True if <code>year</code> is a leap year.

@example
const leapYear = Cesium.isLeapYear(2000); // true