JSON decoding

Brendan Eich brendan at mozilla.org
Fri Oct 20 12:57:28 PDT 2006

On Oct 20, 2006, at 3:51 PM, Bob Ippolito wrote:

> On 10/20/06, Brendan Eich <brendan at mozilla.org> wrote:
>> On Oct 20, 2006, at 3:36 PM, Erik Arvidsson wrote:
>> > If Date is serialized as an ISO strings the process of encoding and
>> > decoding loses information. If Dates are added to JSON then they
>> > should be encoded using new Date(ms). However Dates are not  
>> supported
>> > in JSON today and removing them from JS2 seems OK.
>> ES4 also standardizes Date.parse to accept the same ISO 8601 date
>> strings, so I don't believe any information is lost.
> Even if there wasn't, you can always turn strings into dates the hard
> way as MochiKit does...

Sure.  That was more an FYI (ECMA-262 left Date.parse unspecified, a  
botch that requires browsers to reverse engineer IE JScript's  
Date.parse implementation).

> The important part is that the metadata that it is a date is lost,
> even if there's an easy way to make dates from strings. You have to
> know which strings should be treated as dates.

You're right, but JSON does not provide any way to distinguish this  
case (preserve the bit of metadata you cite).

>> You're right that this automatic encoding of Date objects as ISO
>> strings does not result, when decoding, in Date objects again.
>> Fixing that would require a pass over the decoded structure, or a use
>> of the optional object hook on the enclosing object.  Is this a  
>> problem?
> The object hook would be no good here because it would have to be able
> to find ISO strings by key (or regexing all string values looking for
> dates.. bleh).

The context would have to determine what's a date and what is not.   
Yeah, it's poor, but without extending JSON, what can be done?


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