What is the Best Practice for Encoding Dates in JSON?

Question

When designing a service that returns JSON to the browser (or server side JS), what is the "best" format for encoding dates in the resulting JSON response?

The data property should:

• require as little or no parsing to convert to a Date() object
• be sortable in the JSON representation itself

Returning the number of milliseconds since 1 January 1970 00:00:00 UTC seems like it would be the best option but is not particularly human readable when looking at the raw JSON.

What's preferred in your experience and why?

Answer 1

Personally I'd go with ISO 8601 (e.g. 2011-01-13T14:09Z).

It's well supported by virtually every programming language around, it's fairly easily human readable and, if you absolutely have to roll your own parser/formatter, it's fairly easy to deal with there too. It also has the sortable property you wanted.