test.html

<script src="/build/three.min.js"></script>
<script src="/examples/js/loaders/STLLoader.js"></script>
<script src="/examples/js/controls/OrbitControls.js"></script>

<div id="model" style="width: 500px; height: 500px"> </div>
<div id="model2" style="width: 500px; height: 500px"> </div>

<script type="text/javascript">

window.onload = function() {
    STLViewer("keystone.stl", "model")
    STLViewer("keystone.stl", "model2")
}


function STLViewer(model, elementID) {
    var elem = document.getElementById(elementID)

    var camera = new THREE.PerspectiveCamera(70, 
    elem.clientWidth/elem.clientHeight, 1, 1000);

    var renderer = new THREE.WebGLRenderer({ antialias: true, alpha: true });
    renderer.setSize(elem.clientWidth, elem.clientHeight);
    elem.appendChild(renderer.domElement);

    window.addEventListener('resize', function () {
        renderer.setSize(elem.clientWidth, elem.clientHeight);
        camera.aspect = elem.clientWidth/elem.clientHeight;
        camera.updateProjectionMatrix();
    }, false);

    var controls = new THREE.OrbitControls(camera, renderer.domElement);
    controls.enableDamping = true;
    controls.rotateSpeed = 0.05;
    controls.dampingFactor = 0.1;
    controls.enableZoom = true;
    controls.autoRotate = true;
    controls.autoRotateSpeed = .75;

    var scene = new THREE.Scene();
    scene.add(new THREE.HemisphereLight(0xffffff, 1.5));

    (new THREE.STLLoader()).load(model, function (geometry) {
        var material = new THREE.MeshPhongMaterial({ 
            color: 0xff5533, 
            specular: 100, 
            shininess: 100 });
        var mesh = new THREE.Mesh(geometry, material);
            scene.add(mesh);

        var middle = new THREE.Vector3();
        geometry.computeBoundingBox();
        geometry.boundingBox.getCenter(middle);
        mesh.geometry.applyMatrix(new THREE.Matrix4().makeTranslation( 
                                    -middle.x, -middle.y, -middle.z ) );

        
        var largestDimension = Math.max(geometry.boundingBox.max.x,
                            geometry.boundingBox.max.y, 
                            geometry.boundingBox.max.z)
        camera.position.z = largestDimension * 1.5;

        var animate = function () {
            requestAnimationFrame(animate);
            controls.update();
            renderer.render(scene, camera);
        }; 

        animate();
    });
}


</script>