ds4/module/actor/actor.js

/**
 * Extend the base Actor entity by defining a custom roll data structure which is ideal for the Simple system.
 * @extends {Actor}
 */
export class DS4Actor extends Actor {
  /** @override */
  prepareDerivedData() {
    const data = this.data;
    this._prepareCombatValues(data);
  }

  _prepareCombatValues(data) {
    const hitPointsModifier = getProperty(data, "data.combatValues.hitPoints.modifier") || 0;
    setProperty(
      data,
      "data.combatValues.hitPoints.max",
      data.data.attributes.body.initial + data.data.traits.constitution.initial + 10 + hitPointsModifier
    );

    const defenseModifier = getProperty(data, "data.combatValues.defense.modifier") || 0;
    setProperty(
      data,
      "data.combatValues.defense.value",
      data.data.attributes.body.initial +
        data.data.traits.constitution.initial +
        this._getArmorValue() +
        defenseModifier
    );
  }

  _getArmorValue() {
    return this.data.items
      .filter((item) => ["armor", "shield"].includes(item.type))
      .filter((item) => item.data.equipped)
      .map((item) => item.data.armorValue)
      .reduce((a, b) => a + b, 0);
  }
}