Adding Effects to Pokestar

Quick Reference

Files to modify:

1. src/enums/battleEnums.js - Add effectIdEnum.YOUR_EFFECT entry (ONLY if not exists)
2. src/battle/data/effects.js - Add the effect implementation

DO NOT modify other effects or battleConfig.js unless explicitly asked.

Effect Structure

[effectIdEnum.EFFECT_NAME]: new Effect({
  id: effectIdEnum.EFFECT_NAME,
  name: "Effect Name",
  description: "Description of the effect",
  type: effectTypes.BUFF,        // BUFF, DEBUFF, or NEUTRAL
  dispellable: true,             // Can it be removed by dispell effects?
  effectAdd({ battle, target, source, initialArgs }) {
    // Called when effect is applied
    // initialArgs contains arguments passed when applying the effect
    return {
      // Properties to store for later use in effectRemove
    };
  },
  effectRemove({ battle, target, source, properties, initialArgs }) {
    // Called when effect expires or is removed
    // properties contains what effectAdd returned
    // Clean up any listeners or state here
  },
  tags: [],                      // Optional: ["hazard", "test"]
}),

Properties Pattern

The most important pattern is the properties pattern - return state from effectAdd that you'll need in effectRemove:

effectAdd({ battle, target, source, initialArgs }) {
  return {
    listenerId: battle.registerListenerFunction({...}),
    originalValue: target.getStat("atk"),
    counter: 0,
  };
},
effectRemove({ battle, target, properties }) {
  battle.unregisterListener(properties.listenerId);
}

Event Listener Registration

Use battle.registerListenerFunction for effects (effects don't have a class-level helper):

effectAdd({ battle, target }) {
  return {
    listenerId: battle.registerListenerFunction({
      eventName: battleEventEnum.BEFORE_DAMAGE,
      callback: (args) => {
        // Modify damage or perform logic
        return { damage: Math.floor(args.damage * 0.5) };
      },
      conditionCallback: getIsTargetPokemonCallback(target),
    }),
  };
},
effectRemove({ battle, properties }) {
  battle.unregisterListener(properties.listenerId);
}

Effect Types

Using initialArgs

Effects can receive arguments when applied. Access them in both add and remove:

effectAdd({ battle, target, initialArgs }) {
  const { shield } = initialArgs;
  battle.addToLog(`${target.name} is shielded for ${shield} damage!`);
  return { shieldAmount: shield };
},
effectRemove({ battle, target, initialArgs }) {
  const { shield } = initialArgs;
  // initialArgs persists through the effect's lifetime
}

Common Gotchas

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

1. Event Argument Modification: Return modified values from callbacks to change event behavior:

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

1. State Management: Properties can be mutated during runtime - be careful with shared references.

1. Dispellable Flag: Set dispellable: false for effects that should persist through dispell abilities.

Validation

After implementing an effect, run the effect test suite to validate the implementation:

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

This runs an e2e test that verifies all effects can be applied and removed without throwing errors. If your new effect 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 effect implementation patterns
• add-event-listener skill - Common event types and condition callbacks