Phaser Core

Phaser 4 Core

Set up the foundation of a Phaser game: the Game config, the Scene lifecycle, asset loading, cameras, and passing data between scenes. Targets Phaser 4.2 for new projects; keep an existing Phaser 3.90 project on its pinned major unless the user explicitly asks for a migration.

When to use

• Use when starting a Phaser game, wiring the Phaser.Game config, structuring Scenes, loading assets in preload, or fixing scene transitions and shared state.
• Use when the project has phaser in package.json or import Phaser from 'phaser', and code uses preload()/create()/update().

*When not to use:* movement, velocity, colliders, gravity, or overlap → use phaser-arcade-physics. Complex rigid-body simulation uses Matter physics (a separate concern). For cross-engine save/load patterns use save-systems.

Core workflow

1. Detect the installed major first. Read package.json and the lockfile. Use Phaser 4.2 for new work; do not silently rewrite a Phaser 3 project as Phaser 4.
2. Create the game from a config. new Phaser.Game(config) with type: Phaser.AUTO (WebGL with Canvas fallback), a width/height, and a scene array. The first scene (and any with active: true) starts automatically.
3. Model each screen as a `Scene`. Subclass Phaser.Scene, pass a unique key to super, and implement the lifecycle: init(data) → preload() → create(data) → update(time, delta).
4. Load assets in `preload`, use them in `create`. Queued assets are not available until create. The loader is per-scene; the cache it fills is global.
5. Reset per-run state in `init()`, not the constructor. A scene instance is reused across restarts, so constructor-set fields keep stale values.
6. Move between screens with this.scene.start/launch/switch/sleep/wake. Share data through this.registry (global) or a sibling scene's event emitter.
7. Run and observe. Serve the page, open it, and confirm assets load (watch the Network tab and console) and scenes switch as expected before assuming success.

Patterns

1. Game config + boot (ES module)

// main.js — one Game owns the renderer, loop, cache, and Scene Manager.
import Phaser from 'phaser';
import BootScene from './scenes/BootScene.js';
import PlayScene from './scenes/PlayScene.js';

const config = {
  type: Phaser.AUTO,            // WebGL if available, else Canvas
  width: 800,
  height: 600,
  backgroundColor: '#1d1d28',
  scale: { mode: Phaser.Scale.FIT, autoCenter: Phaser.Scale.CENTER_BOTH },
  scene: [BootScene, PlayScene] // BootScene starts first
};

new Phaser.Game(config);

2. A Scene with the full lifecycle

// scenes/PlayScene.js
import Phaser from 'phaser';

export default class PlayScene extends Phaser.Scene {
  constructor() {
    super('play');                  // unique scene key
  }

  init(data) {
    // Reset run-specific state HERE so restarts start clean.
    this.score = 0;
    this.level = data.level ?? 1;
  }

  preload() {
    // Queue downloads. Not usable until create().
    this.load.image('player', 'assets/player.png');
    this.load.spritesheet('coin', 'assets/coin.png', { frameWidth: 16, frameHeight: 16 });
  }

  create() {
    this.player = this.add.sprite(400, 300, 'player');
    this.scoreText = this.add.text(10, 10, 'Score: 0', { fontSize: '20px', color: '#fff' });
    this.cursors = this.input.keyboard.createCursorKeys();
  }

  update(time, delta) {
    // delta is milliseconds since last frame; divide by 1000 for seconds.
    const speed = 200 * (delta / 1000);
    if (this.cursors.left.isDown)  this.player.x -= speed;
    if (this.cursors.right.isDown) this.player.x += speed;
  }
}

3. Cross-scene data + events

// The registry is a global DataManager shared by every scene.
this.registry.set('coins', 0);                 // in any scene
const coins = this.registry.get('coins');      // read anywhere

// React to registry changes (e.g. a HUD scene listening to gameplay):
this.registry.events.on('changedata-coins', (parent, value) => {
  this.coinText.setText(`Coins: ${value}`);
});

// Talk directly to another running scene via its event emitter:
const ui = this.scene.get('hud');
ui.events.emit('show-message', 'Level cleared!');

4. Scene transitions (pick the right verb)

this.scene.start('gameover', { score: this.score }); // stop this scene, start target
this.scene.launch('hud');        // run a second scene in parallel (overlay HUD)
this.scene.switch('menu');       // sleep this scene, start/wake target
this.scene.pause();              // freeze updates but keep rendering (modal)
this.scene.sleep();              // stop updating AND rendering, keep state for wake

5. A camera that follows the player

this.cameras.main.setBounds(0, 0, 1600, 1200);  // world size
this.cameras.main.startFollow(this.player, true, 0.1, 0.1); // smooth lerp follow
this.cameras.main.setZoom(1.5);

Pitfalls

• Assets are `undefined` in `create`/`update` → you forgot to queue them in preload, or used the wrong key. The loader runs between preload and create.
• State leaks across a restart → you set fields in the constructor. The Scene instance is reused; reset run state in init() and clear arrays on shutdown.
• `this.scene.start` vs `this.scene.launch` → start stops the calling scene; launch runs the target alongside it. Using start for a HUD hides the game.
• `this` is wrong in a callback → arrow functions keep the Scene's this; plain function callbacks need a context argument or .bind(this).
• Phaser 2 tutorials don't work → "States" were renamed to "Scenes" in Phaser 3, and each Scene owns its own systems (input, cameras, tweens) rather than a global Game World.
• Phaser 3 custom pipelines fail in Phaser 4 → Phaser 4 rebuilt the renderer and replaced the old FX/pipeline extension points. Migrate custom shaders and renderer plugins against the Phaser 4 guide; do not mechanically copy internal renderer code.
• Nothing renders / black screen → confirm the canvas mounted, width/height are set, and a scene actually started (check game.scene.dump() output).

References

• For the full scene state machine (pause/resume vs sleep/wake vs stop/start, the restart-state bug, and removing/replacing scenes), read references/scene-flow.md.

Related skills

• phaser-arcade-physics — velocity, gravity, colliders, overlap, and groups.
• input-systems — rebindable, multi-device input architecture (engine-agnostic).
• pixijs-rendering / threejs-scene-setup — other browser rendering stacks.
• platformer / puzzle — genre templates that compose Phaser skills.