---
title: "State machines and game flow"
package: "@phaser-ae/fsm"
tier: Free
version: 3.0.0-4
released: 2026-10-14
updated: 2026-10-20
description: "State machines for everything with modes, from an enemy's patrol, chase and death to the game's own attract, play and game-over flow."
url: https://phaser.io/packs/fsm
site: Phaser - https://phaser.io
---

# State machines and game flow

A brain for every object that has modes, and a phase graph for the game itself. Patrol, chase and dying become three
named states; attract, play, dying and game over become four named phases; and neither needs a tangle of flags.

## What it does

The engine has no entity classes, so an object's behaviour lives in a brain: a plain object of named states, each with
optional `enter`, `tick` and `exit` callbacks. You pass it as `brain` when you spawn the object. Every simulate step the
pack runs the current state's `tick`, and on the handle `h.fsm.go` switches state (calling the old state's `exit` and
the new one's `enter`), `h.fsm.is` tests it and `h.fsm.time` counts the seconds spent in it. Write motion in `tick`,
one-shot effects such as a sound or a shake in `enter`, and clean-up in `exit`.

The game's own flow is a different shape, and `createPhases` handles it. Phases share one context object, and each
lists its way out: edges with a condition, tested in order after the phase's update, or a timed exit after so many
seconds. Changes are queued and applied at the top of the next update, so a phase is never torn down while its own code
is running. A phase can own things, such as a game-over banner, and they are disposed when it ends; timers started in a
phase end with it too. `restart()` takes a phase's restart point, the death-to-respawn edge that skips an intro.

For an attract loop or a cut scene, `createSequence` plays named steps for set times and reports how far through the
current step it is, so a title can cycle logo, demo and high scores and fade between them.

## Features

- **Brains at spawn** — named states with `enter`, `tick` and `exit`, attached with the `brain` spawn field.
- **Time in state** — `h.fsm.time` counts seconds since the last change, for "chase for three seconds, then give up".
- **Typed states** — `game.fsm.define` infers the state names as a union, so a misspelt `go` target is a type error,
  and a missing state at run time is an error that lists the states the brain has.
- **Ticks before collision** — brains run before `collision` in the same frame, so a state change is seen at once.
- **Phase graphs** — guarded edges, timed exits, `restartAt`, `in(...names)` and the previous phase.
- **Owned objects and timers** — `own`, `at` and `every`, all cleared when the phase exits.
- **Sequences** — looping attract cycles or one-shot cut scenes, with `current`, `frac`, `go`, `reset` and `onStep`.
- **Headless, 2D or 3D** — it draws nothing and works in any world.

## Good for

- **Arcade enemies** with patrol, chase, flee and dying states.
- **Bosses with phases**, where each phase is a state with its own attack pattern and an entry flourish.
- **Player controllers** with grounded, jumping and dashing states.
- **Doors, turrets and pickups** that idle, react and then do something else.
- **An arcade game's flow**: attract, play, dying with a respawn, and game over back to attract.
- **Attract modes and cut scenes** as timed steps.

## Make it yours

A brain is just data, so each kind of enemy is a new object of states, and two enemies can share most of a brain. The
pack has no options: compose it, pass `brain` at spawn, and import `createPhases` and `createSequence` (or use
`game.fsm.phases` and `game.fsm.sequence`) when the game needs them.

Two quite different uses: a top-down shooter where every enemy carries a three-state brain that patrols, chases the
player when near and plays a short death; and a game where `fsm` holds no brains at all and only runs the flow, an
attract sequence that loops logo, demo and scores, then play, dying and game-over phases with a timed return.

## A quick look

An enemy with three states, attached at spawn:

```ts
const crab = game.fsm.define<'patrol' | 'chase' | 'dying'>({
    initial: 'patrol',
    states: {
        patrol: { tick: (h, dt) => { h.x += 40 * dt; if (near(h, player)) h.fsm.go('chase'); } },
        chase:  { tick: (h, dt) => moveToward(h, player, 70 * dt) },
        dying:  { enter: h => game.after(0.25, () => kill(h)) },
    },
});
game.spawn({ id: 'crab', x, y, tags: ['enemy'], brain: crab });
```

## Works with

- `collision` — brains tick before it, so a state change counts in the same frame's hits.
- `scoreboard` — score, lives and the high-score table that phases test and reset.
- `wave-plan` — waves, difficulty and the win rule a play phase drives.
- `title-screen` — a title screen drawn for you.
- `flow` — ready-drawn title, pause and game-over scenes, when you do not need your own phases.

## Good to know

- One brain per object: a second `brain()` call replaces the first without calling its `exit`.
- `h.fsm.state` is the state's index, a number; use `is()` or `game.fsm.state(h)` for the name.
- A `go` from inside `enter` works but re-enters at once, so guard against loops. Ticks run in spawn order, with no
  priority.
- Phases and sequences are not stepped for you: call `update(dt)` once a frame. A `go` to a phase with no definition
  enters an empty phase rather than throwing.
- For one behaviour with no branches, a plain simulate step over a tag is simpler.

---

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