add-held-item

name	add-held-item
description	Add held items to the battle system. Use when creating items Pokemon can hold for passive or triggered effects.

Adding Held Items to Pokestar

Quick Reference

Files to modify:

1. src/enums/battleEnums.js - Add heldItemIdEnum.YOUR_ITEM entry (ONLY if not exists)
2. src/config/backpackConfig.js - Add item metadata (name, description) if not exists
3. src/battle/data/heldItems.js - Add the held item implementation

DO NOT modify other held items or battleConfig.js unless explicitly asked.

Held Item Structure

[heldItemIdEnum.ITEM_NAME]: new HeldItem({
  id: heldItemIdEnum.ITEM_NAME,
  itemAdd({ battle, target }) {
    // Called when item is applied to Pokemon
    return {
      // Properties to store for later use in itemRemove
      listenerId: this.registerListenerFunction({...}),
    };
  },
  itemRemove({ battle, target, properties }) {
    // Called when item is removed
    battle.unregisterListener(properties.listenerId);
  },
  itemUse({ battle, target }) {
    // Optional: Logic for when the item is consumed
    // Only required for items with the "usable" tag
  },
  tags: ["berry", "usable"],  // Optional tags for item categorization
}),

Properties Pattern

Return state from itemAdd that you'll need in itemRemove:

itemAdd({ battle, target }) {
  return {
    listenerId: this.registerListenerFunction({...}),
    originalStat: target.getStat("atk"),
    triggered: false,
  };
},
itemRemove({ battle, target, properties }) {
  battle.unregisterListener(properties.listenerId);
}

Event Listener Registration

Held items have a class-level registerListenerFunction method that automatically includes the held item instance:

itemAdd({ battle, target }) {
  return {
    listenerId: this.registerListenerFunction({
      battle,
      target,
      eventName: battleEventEnum.AFTER_DAMAGE_DEALT,
      callback: ({ damage, heldItemInstance }) => {
        // heldItemInstance.data contains the properties
        // Perform item logic
      },
      conditionCallback: getIsTargetPokemonCallback(target),
    }),
  };
},

Example Item Tags

Tag	Description
berry	Berry item, consumed after use
usable	Item can be consumed, requires itemUse method

Common Gotchas

1. Always Clean Up Listeners: Failing to unregister listeners causes memory leaks.

2. Item Data: Name and description come from backpackHeldItemConfig[id], not the HeldItem constructor.

3. Event Argument Modification: Return modified values from callbacks:

   callback: (args) => {
     return { damage: Math.floor(args.damage * 0.5) };
   };
   

4. usable Tag: Items with the usable tag MUST implement itemUse.

5. heldItemInstance: Access stored properties via heldItemInstance.data in callbacks.

Validation

After implementing a held item, run the held item test suite to validate the implementation:

npm test -- src/battle/data/__tests__/heldItems.test.js

This runs an e2e test that verifies all held items can be applied and removed without throwing errors. For items with the usable tag, it also verifies that itemUse can be called. If your new held item causes a test failure, fix the implementation and re-run until tests pass.

See the unit-test skill for more details on testing.

References

• references/pattern-*.md - Common held item implementation patterns
• add-event-listener skill - Common event types and condition callbacks