Bugfix: Datepicker doesn't mark input field invalid if the date is invalid

[rickirunge]

I wanted to use the date picker, with the danish date format "dd/MM/yyyy", and found several issues (#956, #1107, #1430) and also a TODO in the code, all refering to that this was not yet implemented for manual typing in the input field.

One solution I found described in the issues (#956) was to use: https://github.com/dnasir/angular-dateParser, which works perfect - except an error in angular UI datepicker became visible.

If your from the JS set the value of date-field to a date that is invalid (for instance new Date(undefined) or new Date("pizza"), which both return a date object, in the state "Invalid Date"), the field is not marked "invalid".

Fix is simple, right now the code just checks if the value is a date, and then marks is valid. But we just need to also check that the date is actual valid ( isNan(date) return true the date is invalid)

[bekos]

@rickirunge Thx for the PR. LGTM.

About parsing custom formats, is something we can do yet and I don't know if it's going to happen in the near future. For now, the best approach is to use a custom directive for your specific format or use another library like moment.js.

[bekos]

@rickirunge Thx!

[rickirunge]

@bekos as I wrote, I got it all working with the dateParser lib, but then found this other error, and found that that fix would make it all work nicely.

So I'm happy now, and would now switch back to use the official version of Angular UI Bootstrap, instead of my own patched version