--- title: "Turn battle: API" package: "@phaser-ae/turn-battle" tier: Free version: 3.0.0-0 released: 2026-10-19 updated: 2026-10-19 description: "Classic turn-based battles as a state machine over plain data, with speed order, attacks, skills, items, defending, fleeing, an element wheel, criticals and a Break gauge." url: https://phaser.io/packs/turn-battle/api site: Phaser - https://phaser.io --- # Turn battle: API `@phaser-ae/turn-battle` — Turn-based battles as a state machine: speed order, attacks, skills, items, defending, fleeing, an element wheel, criticals and a Break gauge, all data. ## The pack ### `turnBattle` ```ts function turnBattle(): Pack<{ turnBattle: typeof api }> ``` Install the turn-battle API (`game.turnBattle`): the battle rules and the `Battle` state machine. ## Helpers ### `BATTLE_RULES` ```ts const BATTLE_RULES: Readonly ``` The default rules. ### `battleRules` ```ts const battleRules = (o: Partial = {}): BattleRules=> … ``` The default rules with some replaced. ### `breakTurn` ```ts function breakTurn(b: BreakState): boolean ``` A broken fighter's turn comes round: it skips the turn and recovers a full shield. Returns true when a turn was skipped. ### `damage` ```ts const damage = (atk: number, def: number, factor: number, roll: number, rules: BattleRules = BATTLE_RULES): number=> … ``` Damage of one hit: `max(minDamage, round(base(atk, def) × factor × spread))`; `roll` in [0, 1) picks the spread. ### `dropFalls` ```ts const dropFalls = (m: { boss: boolean; dropItemId: string | null }, roll: number, rules: BattleRules = BATTLE_RULES): string | null=> … ``` A foe leaves its drop: always for a boss, else on a roll under `dropChance`. ### `ELEMENT_WHEEL` ```ts const ELEMENT_WHEEL: Readonly> ``` The built-in wheel: what each element beats. `none` is physical and beats nothing. ### `elementFactor` ```ts const elementFactor = (attack: string, target: string, rules: BattleRules = BATTLE_RULES): number=> … ``` The damage multiplier of an attack element against a target element: weak, resisted (the target beats it) or plain. ### `encounterFires` ```ts const encounterFires = (rate: number, roll: number): boolean=> … ``` A random encounter fires on a roll under the rate. ### `fleeSucceeds` ```ts const fleeSucceeds = (roll: number, rules: BattleRules = BATTLE_RULES): boolean=> … ``` A flee succeeds on a roll under `fleeChance`. ### `hitBreak` ```ts function hitBreak(b: BreakState, weak: boolean): boolean ``` A hit that exploits a weakness removes one shield point; at 0 the fighter is BROKEN. Returns whether this hit broke it. ### `isCrit` ```ts const isCrit = (lck: number, roll: number, rules: BattleRules = BATTLE_RULES): boolean=> … ``` A critical hit lands when the roll is under the rules' `critChance(lck)`. ### `isWeak` ```ts const isWeak = (attack: string, target: string, rules: BattleRules = BATTLE_RULES): boolean=> … ``` True when `attack` beats `target` on the wheel. ### `newBreak` ```ts const newBreak = (max: number): BreakState=> … ``` A fresh gauge. A gauge of 0 can never be broken. ### `resolveHit` ```ts function resolveHit(s: HitSpec, rules: BattleRules = BATTLE_RULES): HitResult ``` Resolve one hit from the numbers alone. ### `scaleStats` ```ts function scaleStats(stats: S, difficulty: string, rules: BattleRules = BATTLE_RULES): S ``` Stats scaled by a difficulty: hp and attack times the rules' multiplier (1 for a difficulty it does not list). ### `SKILL_EFFECTS` ```ts const SKILL_EFFECTS: Readonly> ``` The built-in skill effects: damage opponents, heal an ally, guard or haste the user (or the party). ### `turnOrder` ```ts const turnOrder = (entries: ReadonlyArray): E[]=> … ``` Turn order: by speed, highest first; ties go to heroes, then to the order given. Pure and stable. ## Classes ### `Battle` ```ts class Battle ``` A turn-based battle. - `readonly rules: BattleRules` — The rules it resolves by. - `fighters: Fighter[]` — Every fighter, heroes and foes, in the order given. - `round: number` — The round number, 0 before the first. - `order: Fighter[]` — This round's order. - `turn: number` — Index into `order` of the current actor; -1 before the first turn. - `result: BattleResult | null` — How it ended, or null while it runs. - `constructor(defs: readonly FighterDef[], o: BattleOptions)` - `get(id: string): Fighter | undefined` — A fighter by id. - `side(side: Side): Fighter[]` — The fighters of a side, standing or not. - `standing(side: Side): Fighter[]` — The standing fighters of a side. - `get actor(): Fighter | null` — The fighter whose turn it is, or null. - `get done(): boolean` — True once the current actor has taken its turn: `next()` moves on. - `get recovering(): boolean` — True when the current actor is broken and will spend its turn recovering. - `emit(e: BattleEvent): void` — Queue an event (for skill effects of a game's own). - `drain(): BattleEvent[]` — Every event since the last call. - `next(): Fighter | null` — Move to the next fighter's turn (a new round when this one is done) and return it; null when the battle is over. - `targets(user: Fighter, kind: 'foe' | 'ally' | 'downed'): Fighter[]` — The choices for a one-target action: standing opponents, standing allies, or downed allies (a revive). - `reach(user: Fighter, skill: BattleSkill, target?: string): Fighter[]` — Who a skill reaches when `target` (for one-target skills) is chosen: an unknown effect reaches nobody. - `picks(skill: BattleSkill): 'foe' | 'ally' | null` — What a one-target skill asks the player to pick: an opponent, an ally, or nothing (it reaches its targets itself). - `auto(): BattleAction` — What the battle would choose for the current actor. - `act(action: BattleAction): boolean` — The current actor takes its turn. A broken actor recovers instead, whatever is asked. Returns false (and keeps the turn) when the action cannot be done: not enough MP, no such target, an item that did nothing, no fleeing, or the turn already taken. - `hit(from: Fighter, to: Fighter, element: string, power: number): HitResult` — Hit `to` from `from` with an element and extra power, through the rules: crits, the wheel, the gauge, defending. - `heal(from: Fighter, to: Fighter, amount: number): number` — Heal `to` by up to `amount`; a downed fighter is not healed. Returns what was restored. - `snapshot(): BattleSnapshot` — The whole state, as plain data. - `restore(s: BattleSnapshot): void` — Put a snapshot back (the same battle's options are assumed). ## Types ### `BattleAction` ```ts type BattleAction = /** A plain attack on one opponent, with the attacker's element. */ | { kind: 'attack'; target: string } /** A skill; `target` for one-target skills (default the first standing choice). */ | { kind: 'skill'; skill: BattleSkill; target?: string } /** An item: `use` changes the target (pools, flags) and says whether it did anything; nothing done keeps the turn. */ | { kind: 'item'; target: string; name?: string; use(target: Fighter): boolean } /** Defend until the next turn, getting the rules' `defendMp` back. */ | { kind: 'defend' } /** Try to run: the rules' `fleeChance`. */ | { kind: 'flee' } /** Do nothing. */ | { kind: 'wait' } ``` What a fighter does with its turn. ### `BattleEvent` ```ts type BattleEvent = /** A round began, in this order. */ | { type: 'round'; round: number; order: string[] } /** A fighter's turn began. */ | { type: 'turn'; actor: string } /** A broken fighter spent its turn recovering its shield. */ | { type: 'recover'; actor: string } /** A fighter used a skill. */ | { type: 'skill'; actor: string; skill: string } /** A hit landed. */ | ({ type: 'hit'; from: string; to: string; element: string } & HitResult) /** A hit broke its target's shield. */ | { type: 'break'; to: string } /** A fighter fell. */ | { type: 'down'; id: string; by: string } /** A heal restored health. */ | { type: 'heal'; from: string; to: string; amount: number } /** An item was used. */ | { type: 'item'; actor: string; to: string; name: string; hp: number; mp: number } /** A fighter is guarded (defending) until its next turn. */ | { type: 'guard'; to: string } /** A fighter is hasted. */ | { type: 'haste'; to: string } /** A fighter defends. */ | { type: 'defend'; actor: string; mp: number } /** A flee was tried. */ | { type: 'flee'; actor: string; ok: boolean } /** The battle ended. */ | { type: 'end'; result: BattleResult } ``` What happened, in order. ### `BattleOptions` ```ts interface BattleOptions ``` What a battle is made with. - `rules?: Partial` — The rules, over `BATTLE_RULES`. - `rng: () => number` — Random numbers in [0, 1): a game's seeded stream (`() => game.rng.next()`). - `effects?: Readonly>` — Skill effects, over `SKILL_EFFECTS`. - `choose?: (battle: Battle, actor: Fighter) => BattleAction` — Choose an action for a fighter the player does not command (foes, or heroes in an auto battle). Default: attack a random standing opponent. - `canFlee?: boolean` — Can the heroes run. Default true. ### `BattleResult` ```ts type BattleResult = 'win' | 'lose' | 'flee' ``` How a battle ended. ### `BattleRules` ```ts interface BattleRules ``` How a battle is resolved. Every field has a default (`BATTLE_RULES`). - `wheel: Readonly>` — What each element beats (or null): an attack of an element on what it beats is a weakness. Default `ELEMENT_WHEEL`. - `weakFactor: number` — Damage on a weakness. Default 1.5. - `resistFactor: number` — Damage on a target whose element beats the attack's. Default 0.5. - `critFactor: number` — A critical's multiplier. Default 2. - `brokenFactor: number` — What a broken fighter takes. Default 1.5. - `defendFactor: number` — What a defending fighter takes. Default 0.5. - `defendMp: number` — MP a turn spent defending gives back. Default 5. - `hasteFactor: number` — Speed multiplier while hasted. Default 1.5. - `hasteTurns: number` — Rounds a haste lasts after the turn it is cast (counted down on the hasted fighter's own turns); Infinity is the rest of the battle. Default Infinity. - `spread: number` — The damage spread: a hit is the formula times 1 ± spread/2. Default 0.2 (0.9 to 1.1). - `minDamage: number` — The least a hit does. Default 1. - `fleeChance: number` — Chance a flee succeeds. Default 0.6. - `dropChance: number` — Chance a non-boss foe leaves its drop. Default 0.3. - `healAtk: number` — A heal's amount: the skill's power plus this share of the healer's attack. Default 0.5. - `difficulty: Readonly>` — Stat multipliers per difficulty: hp and attack are scaled. Default gentle 0.8, fair 1, cruel 1.25. - `base(atk: number, def: number): number` — The damage formula before the factors: default `atk - def / 2`. - `critChance(lck: number): number` — The chance of a critical from luck. Default `lck / 100`. ### `BattleSkill` ```ts interface BattleSkill ``` A skill as the battle sees it. - `id: string` — Its id, for events. - `name?: string` — Its name, for events. Default the id. - `effect: string` — What it does: a key of the battle's effects (built in: damage, heal, guard, haste). - `power: number` — For damage, added to the user's attack; for a heal, the amount (plus the rules' share of the user's attack). - `element?: string` — Its element. Default `none`. - `mp: number` — MP it costs. - `target: 'one' | 'all' | 'ally' | 'party' | 'self'` — Who it aims at: one foe, all foes, one ally, the party, or the user. ### `BattleSnapshot` ```ts interface BattleSnapshot ``` A battle's whole state, for `snapshot` and `restore`. - `fighters: Fighter[]` — The fighters. - `round: number` — The round number, 0 before the first. - `order: string[]` — This round's order, by id. - `turn: number` — Index into the order of the current actor, -1 before the first turn. - `result: BattleResult | null` — The result, or null while it runs. - `acted: boolean` — The current actor has taken its turn. ### `BattleStats` ```ts interface BattleStats ``` A fighter's six stats. - `hp: number` — Most health. - `mp: number` — Most magic points. - `atk: number` — Attack: added to a skill's power and set against the target's defence. - `def: number` — Defence: cuts the damage taken. - `spd: number` — Speed: who acts first. - `lck: number` — Luck: the chance of a critical hit. ### `BreakState` ```ts interface BreakState ``` The Break gauge of one fighter. - `shield: number` — Shield points left; 0 is broken. - `max: number` — The full gauge. - `broken: boolean` — True while broken: skips its next turn and takes `brokenFactor`. ### `Fighter` ```ts interface Fighter ``` A fighter in battle: plain data. - `id: string` — Unique among the fighters. - `name: string` — Display name. - `side: Side` — The side it fights on. - `stats: BattleStats` — Its stats. - `hp: number` — Health now; 0 is down. - `mp: number` — Magic now. - `element: string` — Its element. - `brk: BreakState` — Its Break gauge. - `defending: boolean` — Defending until its next turn: takes `defendFactor`. - `haste: number` — Rounds of haste left, counted down at the start of each of its own turns (Infinity for the rest of the battle); 0 is not hasted. - `data: unknown` — The game's own data. ### `FighterDef` ```ts interface FighterDef ``` A fighter going into battle. - `id: string` — Unique among the fighters. - `name?: string` — Display name. Default the id. - `side: Side` — The side it fights on. - `stats: BattleStats` — Its stats, gear and difficulty already applied. - `hp?: number` — Health going in. Default full. - `mp?: number` — Magic going in. Default full. - `element?: string` — The element it attacks with and defends as. Default `none`. - `breaks?: number` — Shield points of its Break gauge. Default 0 (never broken). - `data?: unknown` — Anything the game wants to keep with it (a monster definition, a hero id). Kept in snapshots when it is plain data. ### `HitResult` ```ts interface HitResult ``` What one attack does. - `amount: number` — HP removed. - `crit: boolean` — It was a critical. - `factor: number` — The element factor applied. - `weak: boolean` — The element exploited a weakness. ### `HitSpec` ```ts interface HitSpec ``` What an attack takes to resolve. - `atk: number` — Attacker's attack stat, gear included. - `lck: number` — Attacker's luck stat, for the crit roll. - `power: number` — Extra power from a skill; 0 for a plain attack. - `element: string` — The attack's element. - `def: number` — Target's defence stat, gear included. - `element2: string` — Target's element. - `broken: boolean` — Target is broken. - `defending: boolean` — Target is defending. - `rolls: [number, number]` — Two rolls in [0, 1): the spread and the crit. ### `Side` ```ts type Side = 'hero' | 'foe' ``` Which side a fighter is on. ### `SkillEffect` ```ts interface SkillEffect ``` A skill effect: who its `one` and `all` aim at, and what it does to the targets it reaches. - `aim: 'foe' | 'ally' | 'self'` — What a `one` skill of this effect aims at (`all` is that whole side; `self` makes it the user's side): opponents, allies or the user. - `run(battle: Battle, user: Fighter, targets: Fighter[], skill: BattleSkill): void` — Act on the targets through the battle's verbs (`hit`, `heal`, `emit`) or on the fighters' data. ### `TurnEntry` ```ts interface TurnEntry ``` A fighter as the turn order sees it. - `id: string` — Any id. - `spd: number` — Speed. - `hero: boolean` — Heroes act first on a tie. --- ## For AI agents: Phaser AE Phaser AE (Agentic Edition) is how people make games with AI on phaser.io. 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