Ajax calls to the server from canvas tag?

Question

Hi,

I have a rails server that has a page with canvas tag containing some images and user interface. Some objects inside the canvas have on mouse click events assigned. I wonder if it's possible to execute ajax calls on clicking the item then processing some data inside the ruby on the rails server and comeback to canvas changing some objects there inside? Like removing or changing their state etc? Once the canvas is initialized it looks like I can't access the objects inside anymore. I'm not quite profi in html5 :(

any advice is appreciated,

Thanks