lib/linearcalendar.js
function encodeDate(date) {
	if (!(date instanceof Date)) throw new Error('Value not Date: ' + date)
	return (date.getUTCFullYear() * monthsPerYear + date.getUTCMonth()) - yearMonthZero
}
function encodeDate(date) {
	if (!(date instanceof Date)) throw new Error('Value not Date: ' + date)
	return (date.getUTCFullYear() * monthsPerYear + date.getUTCMonth()) - yearMonthZero
}
function encodeDate ( date ) { if ( ! ( date instanceof Date ) ) throw new Error ( 'Value not Date: ' + date ) return ( date . getUTCFullYear ( ) * monthsPerYear + date . getUTCMonth ( ) ) - yearMonthZero }
get linearValue from Date object
get linearValue from Date object