ISO/JSON date format timezone questions

Lars T Hansen lth at
Mon Jul 16 17:18:30 PDT 2007

On 7/16/07, Lars T Hansen <lth at> wrote:
> On 7/13/07, doekman at <doekman at> wrote:
> > Hi,
> > I was wondering about two things involving timezones.
> >
> > The proposal "Date and time improvements" is defining the
> > Date.toISO():String method.
> >
> > It's unclear to me in what timezone the date should
> > be serialized in: local timezone or UTC. Although it's semantically
> > correct to allow both and let the implementors decide, but I think
> > that would be "not a good thing".
> >
> > I prefer is to be serialized in UTC (with the Z suffix).
> I agree.  I'll update the proposal.

Actually the proposal states (last sentence on the page) that the
timezone field is always present and never Z.  It's possible that is
an external requirement; I'll have to look into it further.


> > The
> > downside of this is, all json users will have to support time-zones.
> As opposed to the current situation, when they have no idea what the
> time stamp means? ;-)
> > The advantage is, you can truncate two arbitrary json-date strings,
> > and compare them, even if the dates are serialized in different
> > timezones.
> >
> > The other question is concerning the "JSON encoding and decoding"
> > proposal. Is the Date serialization using the (fixed) formatting
> > of, or is it using the toISO method,
> > mentioned above?
> JSON has no syntax for time or date data, according to the grammar on
>  The code you reference does format dates as strings,
> however, and it contains a comment which states that eventually dates
> will be formatted according to Date.prototype.toISOString().  This
> seems natural to me, as the ISO date format is unambiguous and
> compact.
> So far the committee has been happy not to write any code for
> toJSONString, instead (informally) incorporating the code on
> by reference.  That may or may not change in the future.
> --lars

More information about the Es4-discuss mailing list