Problem with Simplifying models using SimplifyModifier

Questions
1

I am trying to reduce the number of vertices/meshes in my model by using the SimplifierModifier module. I copied the three js example and ran it with my own gltf model. But I keep getting an error:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'clone')

which originates from the .clone() line in the example:

new GLTFLoader().load( 'test.glb', function ( gltf ) {

const mesh = gltf.scene.children[ 0 ];
mesh.position.x = - 3;
mesh.rotation.y = Math.PI / 2;
scene.add( mesh );

const modifier = new SimplifyModifier();
const simplified = mesh.clone();
simplified.material = simplified.material.clone();
simplified.material.flatShading = true;
const count = Math.floor( simplified.geometry.attributes.position.count * 0.875 ); // number of vertices to remove
simplified.geometry = modifier.modify( simplified.geometry, count );

simplified.position.x = 3;
simplified.rotation.y = - Math.PI / 2;
scene.add( simplified );

render();
}

I thought that I might be using an old version so here is my three js versioning:

<script async src="https://unpkg.com/es-module-shims@1.3.6/dist/es-module-shims.js"></script>
    <script type="importmap">
    {
        "imports": {
            "three": "https://unpkg.com/three@0.143.0/build/three.module.js"
        }
    }
</script>  

<script type="module">

      import * as THREE from 'three';

      import { OrbitControls } from 'https://unpkg.com/three@0.143.0/examples/jsm/controls/OrbitControls.js';
      import { GLTFLoader } from 'https://unpkg.com/three@0.143.0/examples/jsm/loaders/GLTFLoader.js';
      import { SimplifyModifier } from 'https://unpkg.com/three@0.143.0/examples/jsm/modifiers/SimplifyModifier.js';
</script>

But the error is still the same which seems to be stating that there is no function called clone().

2

Much of your code appears to be missing in the example above.

I think the most likely cause is that whatever object you’re working with is not a THREE.Mesh instance. The result of a GLTFLoader loading callback, e.g. gltf.scene is a THREE.Group. To simplify meshes in that group (there may be many) you’ll need to use traverse() and simplify each of them.