I posted the second answer to a question and referenced the first answer in my answer. The user who posted the first answer has since deleted their answer. I'd like to add the info from that first (now deleted) answer to my answer. Is there a way for me to view that deleted answer?
The question is here: Incorrect date displayed with Esri JavaScript API v.2.6
I think you can see this once you get enough rep or are a mod.
You've got it mostly right, you just need to change the code to reflect the correct time zone.
Since the feature you're reading from is a UTC timestamp, the JavaScript code is converting to your timezone, which (assuming you're in the US) will be 4 to 7 hours earlier than midnight of 8/15/2007, which is why it's returning one day earlier.
