JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//cdn.rawgit.com/mrdoob/three.js/master/build/three.min.js"></script>

CSS

body {
	  margin: 0;
}

JavaScript

var camera, scene, renderer;
var geometry, material, mesh, light;

init();
animate();

function init() {

    camera = new THREE.PerspectiveCamera( 70, window.innerWidth / window.innerHeight, 0.01, 10 );
    camera.position.z = 1;

    scene = new THREE.Scene();

    geometry = new THREE.BoxGeometry( 0.2, 0.2, 0.2 );
    material = new THREE.MeshNormalMaterial();

    mesh = new THREE.Mesh( geometry, material );
    mesh.castShadow = true;
    scene.add( mesh );

    renderer = new THREE.WebGLRenderer( { antialias: true } );
    renderer.setSize( window.innerWidth, window.innerHeight );
    renderer.shadowMap.enabled = true;
    document.body.appendChild( renderer.domElement );
    
    var floor = new THREE.Mesh(
            new THREE.PlaneBufferGeometry( 10, 10 ),
            new THREE.ShadowMaterial({ color: "red" })
        );
        floor.position.y = -0.5;
        floor.rotation.x = -0.5 * Math.PI;
        floor.receiveShadow = true;
        scene.add(floor);

        light = new THREE.DirectionalLight();
        light.position.set( -0.2, 0.6, 0.2 );
        light.castShadow = true;
        light.shadow.camera.near = 0.5;
        light.shadow.camera.far = 500;
        light.shadow.camera.left = -0.2;
        light.shadow.camera.right = 0.2;
        light.shadow.camera.top = 0.2;
        light.shadow.camera.bottom = -0.2;
        scene.add( light );
        scene.add( new THREE.CameraHelper( light.shadow.camera ) );
        
    // follow the mesh
    light.target = mesh;
}

function animate() {

    requestAnimationFrame( animate );
    
    var t = 2 * Math.PI * (Date.now() % 10000) * 0.0001;
    
    mesh.position.x = Math.sin (t);

		// follow the mesh
    light.position.x = mesh.position.x;

    mesh.rotation.x += 0.01;
    mesh.rotation.y += 0.02;

    renderer.render( scene, camera );

}