I am trying to make a character sheet for some tabletop RPG's on HTML/CSS/JS with Node.JS for practise.
Context-wise: The game system I use awards players XP that can be spent at incremental costs for abilities. There's no level up system, as much as something akin to buying credits and points.
I know how to do this within the scope of JS and just using a check from XP costs and subtraction from the total, and preventing/refusing something if the cost is higher than what they have.
However, I am not sure how to do this for Serverside Validation -- Espically in regards to someone being Malicious and editing the javascript file on their end to either give themselves more experience/xp/resources to spend or change the value of a skill up per level.
How exactly do you validate if someone is using the XP they have at the values that it's supposed to be done at the server end?
Assuming you mean editing the client-side file...
You cannot be sure. In my opinion (which may be incorrect), the best way would be to keep track of the enemies killed on the client-side and send a request to the server with details about the enemy. If the server detects something impossible (for example, 30 enemies killed in 2 seconds with the simplest weapons), then it will not accept it. I don't know of any other ways.