Or, on mousedown store the X and Y coordinates - then when you come to draw each object you can test if the mouse clicked on that area.

You can also store store the x and y of the mouse in mousemove so when you draw the object if the mouse is above it you can draw a highlight or whatever to indicate to the user that they can click on that object.

As an aside - the FPS says 10 - have you limited the game to 10 FPS? Or have you got really low spec machine?