Substracting Dates in Javascript return a negative number

I am using the TimeTracker.js from link text to track Page Load times and put them in Google Analytics. Basically what it does is record a start time, and once the page loads it records a end time and then subtracts. These are recored using (new Date()).getTime().

Everything works fine except for instances where the time difference is betwe开发者_Python百科en 0-100ms. Here I get a massive negative numbers such as -17,183,398,582. Does anyone know what is causing this? Is it got to do with the way Javascript is handling the date substraction or is it something to do with Analytics?

Any help much appreciated. Thanks

Just a guess, but that negative number sounds like it could be linked to Unix epoch time. Example:

var currentTime = new Date().getTime();

currentTime will hold a number such as 1289985468 which represents "GMT: Wed, 17 Nov 2010 09:17:48 GMT".

Perhaps there's a bug in that code you're using.