I dont know how to make proper collision with jumping and how to not allow the player to jump more than once.
It seems like you are trying to use a boolean value
canJump – how does it currently work?
This is a common approach – or using a jump counter, which allows a double-jump but not a triple…
I have implemented a working jump and stage but under a different, but public directory called platformer2
Great! So is your question resolved?
I have another problem but I am not at home to update the code