Add Duration.fromHTMLTime()

Value of HTML’s <input type="time"> have below patterns:

• hh:mm
• hh:mm:ss
• hh:mm:ss.S
• hh:mm:ss.SS
• hh:mm:ss.SSS

These are expressed as below regular expression:

/^(\d{2}):(\d{2})(:(\d{2}))?(\.(\d{1,3}))?$/

cf. https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#times

My idea

Not tested

Implemention

function fromHTMLTime (text) {
  const matched = text.match(/^(\d{2}):(\d{2})(:(\d{2}))?(\.(\d{1,3}))?$/)

  if (!matched) {
    return Duration.invalid('unparsable', `the input "${text}" can't be parsed as HTML time`)
  }

  const getValue = index => matched[index] ? Number(matched[index]) : 0
  const hours = getValue(1)
  const minutes = getValue(2)
  const seconds = getValue(4)
  const milliseconds = getValue(6)
  return Duration.fromObject({
    hours,
    minutes,
    seconds,
    milliseconds
  })
}

Usage example

<input type="time" id="time" value="13:30">

const timeElement = document.getElementById('time')
const value = timeElement.value  // "13:30"
const duration = Duration.fromHTMLTime(value)

[icambron]

A couple thoughts on this:

• It’s not clear to me that HTML time is meant to specify a duration, as opposed to a specific time on some (externally-provided) date, i.e. it seems like 13:30 means the time, as opposed to a period of 13 hours and 30 minutes.
• As a time, it’s just an ISO time and the fromISO method handles, though of course it returns a DateTime, not a Duration

I’m not against providing ISO-like parsing for durations, I just don’t think it really has much to do with HTML Time.

[thomas-darling]

Hmm, on a second thought, I actually agree with @icambron regarding the name.

The best name for this would be fromISOTime(...) - and then I’d suggest we also add a corresponding toISOTime(), so we can do a full roundtrip in this format.

This does raise a question though: While all ISO times can be represented as durations, not all durations can be represented as ISO times, as that format is limited to 24 hours. I think the solution here is to simply return null if toISOTime() is called on a duration that is longer than 24 hours. This would be consistent with the current behavior, when such methods are called on an invalid duration.

Also note that according to https://en.wikipedia.org/wiki/ISO_8601#Times, the time format has changed slightly in the latest version of the spec. Basically, it may now start with a T - and if the value could be confused with a date, the T is required.

So, the format is essentially Thh[mm][ss][.sss] in the short form and [T]hh[:mm][:ss][.sss] in the extended form. Maybe toISOTime() should accept options for whether to omit the T when possible, and whether to use the short or extended form - but on the other hand, the pragmatic choice might be to just always use the form hh:mm[:ss][.sss]