JavaScript Date : How to get working hours between two dates?

function getWorkingHoursBetween(d1,d2)
{
var workingDays = 0;
var daysInbetween = (d2.getTime() - d1.getTime())/(1000 * 3600 * 24);
var d3, iDay;
for(var i=0;i<=daysInbetween;i++)
{
d3 = new Date(d1);
d3.setDate(d3.getDate() + i);
iDay = d3.getDay();
if(iDay !=0 && iDay!=6)
{
workingDays++;
}
}
return (workingDays*9); //9 being the working hours per day
}