Date.toString() should have a variant that returns rfc3339

[DartBot]

This issue was originally filed by sammcca...@google.com

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Date.toString() currently returns something that is almost RFC3339 (it uses the variant with a space instead of 'T' as a separator).

However it's documented as a human-readable string and so I don't want to rely on that.

Could we have a method that explicitly returns a RFC3339 date (with 'T')?

[dgrove]

cc @floitschG.
Removed Type-Defect label.
Added Type-Enhancement, Area-Library, Triaged labels.

[DartBot]

This comment was originally written by @chrisbu

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It would be useful to be able to simply convert a Date to a string format required by browser cookie "expires" parameter, similar to the old javascript toGMTString() function.

From Florian via the mailing list: http://goo.gl/HbJUx:
Note: toGMTString is deprecated and should be replaced with toUTCString.
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/toGMTString

toUTCString is not completely specified, and might not return an rfc1123/rfc822 string:
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/toUTCString