What problem are you trying to solve?

Now that Temporal is on its way to stage 4, it is worth considering how <input type="date">, <input type="time">, <input type="week">, <input type="month"> could integrate with this API.

What solutions exist today?

Getting the value of a date input with valueAsDate returns a Date object. The value of a date input can be set by providing a Date object to valueAsDate. Converting between a Date object and Temporal is possible but far from ideal. valueAsNumber returns the number of milliseconds since the Unix epoch, which is also problematic. The optimal approach at the moment is working with the string value of .value and converting using Temporal.PlainDate.from()/ Temporal.PlainDateTime.from() / Temporal.PlainTime.from().

How would you solve it?

Previous discussion: tc39/proposal-temporal#107 Below is the strawman from that thread updated with the current syntax (the Civil prefix has been changed to Plain).

Add a valueAsTemporal getter/setter to HTMLInputElement
<input type=date> accepts/returns PlainDate
<input type=time> accepts/returns PlainTime
<input type=datetime-local> accepts/returns PlainDateTime
<input type=month> accepts/returns PlainYearMonth

<input type=week> does not have a mapping.

Alternatively, separate valueAsPlainDate, valueAsPlainTime, valueAsPlainDateTime, valueAsPlainYearMonth.