What the heck is IE new Date(string) doing?

Question

Ok so QA gave me this bug where if a date had a single character starting the month, day or year part of the date (formatted MM/dd/yyyy), that (ONLY in IE) it would parse the date but change it.. So digging around and sure enough its being VERY weird..

This is some sample code of what I am talking about in IE

$("#dates").append("<li>04/30/2012 = " + new Date("04/30/2012").toString()+"</li>");
$("#dates").append("<li>a04/30/2012 = " + new Date("a04/30/2012").toString() +"</li>");
$("#dates").append("<li>b04/30/2012 = " + new Date("b04/30/2012").toString() +"</li>");
$("#dates").append("<li>c04/30/2012 = " + new Date("c04/30/2012").toString() +"</li>");
$("#dates").append("<li>d04/30/2012 = " + new Date("d04/30/2012").toString() +"</li>");
$("#dates").append("<li>e04/30/2012 = " + new Date("e04/30/2012").toString() +"</li>");
$("#dates").append("<li>04/a30/2012 = " + new Date("04/a30/2012").toString() +"</li>");
$("#dates").append("<li>04/b30/2012 = " + new Date("04/b30/2012").toString() +"</li>");
$("#dates").append("<li>04/c30/2012 = " + new Date("04/c30/2012").toString() +"</li>");
$("#dates").append("<li>04/d30/2012 = " + new Date("04/d30/2012").toString() +"</li>");
$("#dates").append("<li>04/e30/2012 = " + new Date("04/e30/2012").toString() +"</li>");
$("#dates").append("<li>04/30/a2012 = " + new Date("04/30/a2012").toString() +"</li>");
$("#dates").append("<li>04/30/b2012 = " + new Date("04/30/b2012").toString() +"</li>");
$("#dates").append("<li>04/30/c2012 = " + new Date("04/30/c2012").toString() +"</li>");
$("#dates").append("<li>04/30/d2012 = " + new Date("04/30/d2012").toString() +"</li>");
$("#dates").append("<li>04/30/e2012 = " + new Date("04/30/e2012").toString() +"</li>");

And here is what IE outputs

•04/30/2012 = Mon Apr 30 2012 00:00:00 GMT-0500 (Central Daylight Time)
•a04/30/2012 = Sun Apr 29 2012 20:00:00 GMT-0500 (Central Daylight Time)
•b04/30/2012 = Sun Apr 29 2012 21:00:00 GMT-0500 (Central Daylight Time)
•c04/30/2012 = Sun Apr 29 2012 22:00:00 GMT-0500 (Central Daylight Time)
•d04/30/2012 = Sun Apr 29 2012 23:00:00 GMT-0500 (Central Daylight Time)
•e04/30/2012 = Mon Apr 30 2012 00:00:00 GMT-0500 (Central Daylight Time)
•04/a30/2012 = Fri Apr 29 -2012 20:00:00 GMT-0500 (Central Daylight Time)
•04/b30/2012 = Fri Apr 29 -2012 21:00:00 GMT-0500 (Central Daylight Time)
•04/c30/2012 = Fri Apr 29 -2012 22:00:00 GMT-0500 (Central Daylight Time)
•04/d30/2012 = Fri Apr 29 -2012 23:00:00 GMT-0500 (Central Daylight Time)
•04/e30/2012 = Sat Apr 30 -2012 00:00:00 GMT-0500 (Central Daylight Time)
•04/30/a2012 = Sun Apr 29 2012 20:00:00 GMT-0500 (Central Daylight Time)
•04/30/b2012 = Sun Apr 29 2012 21:00:00 GMT-0500 (Central Daylight Time)
•04/30/c2012 = Sun Apr 29 2012 22:00:00 GMT-0500 (Central Daylight Time)
•04/30/d2012 = Sun Apr 29 2012 23:00:00 GMT-0500 (Central Daylight Time)
•04/30/e2012 = Mon Apr 30 2012 00:00:00 GMT-0500 (Central Daylight Time)

There is some weird hour add thing going on, except if you add a character to the day part of the format, then it flips the year to BC (from 2012 to -2012???)

We use date pickers so the chance of this happening is pretty limited (but you know QA guys right ;-)... ) So how have others handled this kind of very odd behavior? (FYI: I checked out moment, but it takes a MM/dd/yyyy date and just passes it down to the browsers date parser, so no dice there.

Answer 1

It looks like maybe it's being interpreted as military timezone semantics A-Z.

https://www.rfc-editor.org/rfc/rfc822#section-5.2

http://en.wikipedia.org/wiki/List_of_military_time_zones