Unable to access GLTF properties

I was able to load a static model that I exported using Blender as a .gltf file. At first, I tried .glb, but it would not load because there was a missing DRACOLoader regardless of whether I instantiated one myself or not. I rigged the model in Blender and would like to be able to access the bones and then have posing controlled by user keyboard input. However, I cannot access the rig at all in Three.js. I keep getting “cannot read property of undefined” errors. This is what I have right now regarding loading the model:

    const modelLoader = new GLTFLoader();

    modelLoader.load('/models/fm.gltf', (gltf) => {
        let model = gltf.scene;

        const mats = gltf.scene.getObjectByName('materials');
        let piece = new THREE.SkinnedMesh(model, mats);
        let skelHelper = new THREE.SkeletonHelper(piece);

The GLTF loader is imported above this section. I have also tried just accessing the different properties and get the same error.