Whoops, I missed the original issue, which was that setInterval needs to be told its this object.
So change this: this.interval = setInterval(function(){ $.log('datascape.move : mouseX = ' + this.mouseX); }, 1000); to this: var self = this; this.interval = setInterval(function(){ $.log('datascape.move : mouseX = ' + self.mouseX); }, 1000);