RPGMakerMV pattern for observing changes to player inventory.

ObserverPattern.js

//=============================================================================
// Observer Pattern                                                             
//=============================================================================


//This creates an observer in RPGMaker MV
//This is an example of checking whether an item exists on an observer


(function() {

  var parameters = PluginManager.parameters("ObserverPattern");
  
  function Setup() {
    'use strict';
    //Static class for monitoring items
    class ItemObserver {

      static startObserver() {
        this._itemList = [];
        this.update();
      }

      static update() {
        this.monitorUpdates();
        this.requestUpdate();
      }

      static requestUpdate() {
        requestAnimationFrame(this.update.bind(this));
      }

      static monitorUpdates() {
        if(!this.listMatch()) {
          console.log("Item List Updated");
          this.itemList = $gameParty.allItems();
        }
      }

      static listMatch() {
        if($gameParty !== null) {
          let items = $gameParty.allItems();
          for(let i = 0; i < items.length; i++) {
            if(this.itemList[i] === undefined  || this.itemList[i] !== items[i])
              return false;
          }
          return true;
        }
        return true;
      }

      static set itemList(itemList) {
        this._itemList = itemList;
      }

      static get itemList() {
        return this._itemList;
      }
    }

    //Start Observer Update Method
    ItemObserver.startObserver();
  }
  Setup(); 
})();