Implementation of disabled elements for foundation datepicker project https://github.com/najlepsiwebdesigner/foundation-datepicker/

foundation-datepicker-disabled.js

// implementation of disabled form fields
var nowTemp = new Date();
var now = new Date(nowTemp.getFullYear(), nowTemp.getMonth(), nowTemp.getDate(), 0, 0, 0, 0);
var checkin = $('#dpd1').fdatepicker({
	onRender: function (date) {
		return date.valueOf() < now.valueOf() ? 'disabled' : '';
	}
}).on('changeDate', function (ev) {
	if (ev.date.valueOf() > checkout.date.valueOf()) {
		var newDate = new Date(ev.date)
		newDate.setDate(newDate.getDate() + 1);
		checkout.update(newDate);
	}
	checkin.hide();
	$('#dpd2')[0].focus();
}).data('datepicker');
var checkout = $('#dpd2').fdatepicker({
	onRender: function (date) {
		return date.valueOf() <= checkin.date.valueOf() ? 'disabled' : '';
	}
}).on('changeDate', function (ev) {
	checkout.hide();
}).data('datepicker');

He means that <= and >= should be changed to their actual symbols, now it has been sanitized.

Line 5 mentions an ID. How would the code change if a document had multiple datepickers with a class, but no IDs? (This setup works fine until there comes the time to disable past dates.) Thank you.

gist should be fixed now, for examples please check example file in datepicker repository:
http://github.com/najlepsiwebdesigner/foundation-datepicker

Does this example from the docs work with the latest version of Foundation? I'm getting an error, because date is null.

Change this:
if (ev.date.valueOf() > checkout.date.valueOf()) {
var newDate = new Date(ev.date)
newDate.setDate(newDate.getDate() + 1);
checkout.update(newDate);
}
checkin.hide();

To this:
if(ev.date){
if (ev.date.valueOf() > checkout.date.valueOf()) {
var newDate = new Date(ev.date)
newDate.setDate(newDate.getDate() + 1);
checkout.update(newDate);
checkin.hide();
}
}

https://gist.github.com/onionstand/b006d424c220c412c7c6fae809d2f67a