[AlexanderK]

Thanks for the help again cbk1994. I managed to get most of my Inventory done, as it is a weapon and I can use triggerserver and triggerclient without problems.
However I still can't access my player. itemfunctions from normal NPCs . Even though I copied your suggestion and only changed a few minor things, I get this error:

Script: Function -ItemServerFunctions.showCategories not found at line 10 in script of npcs[13] (in level tilestest.nw at pos (32, 18))

I have no idea what the problem is, as the player has this weapon...

Here is the script of the NPC.

PHP Code:

 //#Clientside
  function onCreated() 
 {
 this.setshape(1,32,64);

 }
function onPlayerChats() {
  temp.tokens = player.chat.tokenize();
  if (tokens[0]=="/getcategories") 
  (@"-ItemServerFunctions").showCategories(this);

} 


This is the script of the weapon -ItemServerFunctions

PHP Code:

function onActionServerSide() {

  if(params[0]=="getCategories") {
    temp.categories=player.getCategories();
    triggerClient("gui", this.name, categories);
  }
  
  if(params[0]=="addItem") {
    player.addItem(params[1], params[2], params[3], params[4], params[5], params[6]);
  }
  
 }

//#CLIENTSIDE

public function showCategories(npcToUpdate) {
  this.npcToUpdate = npcToUpdate;
  triggerServer("gui", this.name, "getCategories");
}

public function addItem(category,itemname,equippable,droppable,usable,quantity) {
  triggerServer("gui", this.name, "addItem", category, itemname, equippable, droppable, usable, quantity);
}

function onActionClientSide(categories) {
 this.npcToUpdate.chat="Categories: " @ categories.size() @ " first category: " @ categories[0][0];
} 


Man... All these interactions between different objects and sides is so complicated.