using getProjectedLocation with user provided lat,long doesn’t work

This works for me:

        var myLocation = new Position.Location(
            {
                :latitude => 45.00,
                :longitude => 45.00,
                :format => :degrees
            }
        );
  
        System.println("Origin:  " + myLocation.toDegrees()[0] + "  /  " + myLocation.toDegrees()[1] ); 
            
        var newLocation = myLocation.getProjectedLocation(Math.PI/2, 10000);
        System.println("Projected:  " + newLocation.toDegrees()[0] + "  /  " + newLocation.toDegrees()[1] ); 

your pos variable is an array. It needs to be a Location, like in @mcinner1's example

I seem to have a problem with the bearing too, it should be from London to Glasgow as shown in the map from the leaflet mapping website but its facing the wrong direction. I’m using the haversine formula which returns 147 in degrees and 2.588 in radians which according to leaflet is correct but on the screen using  getProjectedLocation to create a line of points it returns this so I can only assume the bearing is incorrect:

To me it looks you're 180 degrees off. From the map it looks like 147+180=227 is just about right.

Or let's put it this way, IMHO 147 is the bearing from Glasgow to London

Ok, let me see if that fixes things

Ok, it didn’t work, heres the code:

bearing = (Math.atan2(Math.sin(lon2-lon1)Math.coslat2),Math.cos(lat1) *Math.sin(lat2)- Math.sin(lat1)*Math.cos(lat2)*Math.cosLon2-lon1))) + 180;

I added the 180 at the end after your suggestion,both pairs of lat,lons are in radians. 

Then I perform:

Math.toDegrees(bearing)

to see what it is in degrees as I find 0 to 360 less confusing than radians

then I put it back to radians in a different function to use in getProjectedLocation

Math.toRadians(bearing);

Well for sure if bearing is in radian then you need to add Pi and not 180. However if my theory is correct then IMHO the right thing to do is to switch lat1 and lat2, lon1 and lon2