There's actually a slight bug when overriding parseDate() on a Pikaday instance in that the defaultDate is parsed from a bound input's value by default in the Pikaday constructor using the normal parseDate(), before the instance's parseDate() is updated with a custom function. I could have added `parser` and `formatter` options and attempted to call these functions from toString() and parseDate() but I thought this too much work for little gain. Overriding prototype methods is a simple enough solution for users who want to use other JS Date libraries other than moment.js.