mvhax.js

const getScene = (modelViewerElement) => {
  return modelViewerElement[Object.getOwnPropertySymbols(modelViewerElement)[3]];
};

const getCameraControls = (modelViewerElement) => {
  return modelViewerElement[Object.getOwnPropertySymbols(modelViewerElement)[21]];
};

const modelViewer = document.querySelector('model-viewer');
const scene = getScene(modelViewer);
const cameraControls = getCameraControls(modelViewer);

const animate = () => {
  // Camera object
  const camera = scene.camera;
  // Turntable object
  const pivot = scene.pivot;

  // Animation example:
  pivot.rotation.y += Math.PI / 32.0;
  
  // Always mark the scene as "dirty" so that it renders again:
  scene.isDirty = true;

  requestAnimationFrame(animate);
};

animate();