As is, your page does not recognize when a player has run out of money. It is possible for the user to play your slots game even after the number of credits becomes zero, and the credits can become negative as a result. Any smart casino owner would put a stop to this immediately. Add code to SpinSlots that disallows a spin if the player's credits have reached 0. In particular, the existing code for simulating the spin and displaying the results should only be executed if the player has money?