source.js

let scene, camera, renderer, cube;
function init() {
    scene = new THREE.Scene();
    camera = new THREE.PerspectiveCamera(
        75,
        window.innerWidth / window.innerHeight,
        0.1,
        1000
    );
    camera.position.z = 5;

    renderer = new THREE.WebGLRenderer({ antialias: true });
    renderer.setSize(window.innerWidth, window.innerHeight);
    document.body.appendChild(renderer.domElement);

    const geometry = new THREE.BoxGeometry(2, 2, 2);
    // material - a simple blue color
    // const material = new THREE.MeshBasicMaterial({ color: 0x0000ff });

    // material - a box texture
    const texture = new THREE.TextureLoader().load('textures/box.jpg');
    const material = new THREE.MeshBasicMaterial({ map: texture });
    cube = new THREE.Mesh(geometry, material);

    scene.add(cube);
}

function animate() {
    requestAnimationFrame(animate);
    cube.rotation.x += 0.01;
    cube.rotation.y += 0.01;
    renderer.render(scene, camera);
}

function onWindowResize() {
    camera.aspect = window.innerWidth / window.innerHeight;
    camera.updateProjectionMatrix();
    renderer.setSize(window.innerWidth, window.innerHeight);
}

window.addEventListener('resize', onWindowResize, false);

init();
animate();