text: function update() {
  
      // console.log('lifecycle :', 'update demo scene');
  
      this.$.world.system('previous', [], this.systems.common.previous);
      this.$.world.system('timeout', ['timeout'], this.systems.common.timeout);
      this.$.world.system('commands', ['commands'], this.systems.common.commands);
      this.$.world.system('state', ['state'], this.systems.common.state);
      this.$.world.system('forces', ['forces'], this.systems.common.forces);
      this.$.world.system('velocity', ['position', 'velocity'], this.systems.common.velocity);
      this.$.world.system('fade', ['fade'], this.systems.common.fade);
      this.$.world.system('hitbox', ['hitbox', 'position', 'previous'], this.systems.common.hitbox);
      this.$.world.system('velocity', ['position', 'velocity'], this.systems.common.velocity);
      this.$.world.system('spritesheets', ['images'], this.systems.common.spritesheets);
  
      this.$.camera.update(this.delta);
      this.$.interface.update(this.delta);
  }
  
  export {update};
  