How Do I Convert a Unix Timestamp to ISO 8601 in JavaScript?

Assuming your timestamp is in milliseconds (or you can convert to milliseconds easily) then you can use the Date constructor and the date.toISOString() method.

var s = new Date(1331209044000).toISOString();
s; // => "2012-03-08T12:17:24.000Z"

If you target older browsers which do not support EMCAScript 5th Edition then you can use the strategies listed in this question: How do I output an ISO 8601 formatted string in JavaScript?