Three.js - Why is the shadow of these items looking like this?

I'm learning about three.js.

I make a example to practise but the shadow of the items is looking wrong or stranger.

Should be like this (this image is of a old tutorial):

And the code is this:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/89/three.js"></script>

<div id="WebGL-salida">
</div>

<script type="text/javascript">
  $(function() {
    var scene = new THREE.Scene();

    var camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 0.1, 1000);

    var renderer = new THREE.WebGLRenderer();

    var color = new THREE.Color("rgb(200, 250, 250)");
    renderer.setClearColor(new THREE.Color(color));
    renderer.setSize(window.innerWidth, window.innerHeight);

    renderer.shadowMap.enabled = true;
    renderer.shadowMap.type = THREE.PCFSoftShadowMap; // default THREE.PCFShadowMap


    var ejesAyuda = new THREE.AxesHelper(20); //son los ejes de ayuda creo
    scene.add(ejesAyuda);

    var planeGeometry = new THREE.PlaneGeometry(60, 20);

    var planeMaterial = new THREE.MeshLambertMaterial({
      color: 0xcccccc
    });

    var plane = new THREE.Mesh(planeGeometry, planeMaterial);

    plane.receiveShadow = true;


    plane.rotation.x = -0.5 * Math.PI; // -90º
    plane.position.x = 15;
    plane.position.y = 0;
    plane.position.z = 0;

    scene.add(plane);


    var cubeGeometry = new THREE.CubeGeometry(4, 4, 4);


    var cubeMaterial = new THREE.MeshLambertMaterial({
      color: 0xff0000
    });
    var cube = new THREE.Mesh(cubeGeometry, cubeMaterial);

    cube.castShadow = true; //con esto le indicamos que queremos que emita sombra

    cube.position.x = -4;
    cube.position.y = 3;
    cube.position.z = 0;

    scene.add(cube);

    var sphereGeometry = new THREE.SphereGeometry(4, 20, 20);
    var sphereMaterial = new THREE.MeshLambertMaterial({
      color: 0x7777ff
    });
    var sphere = new THREE.Mesh(sphereGeometry, sphereMaterial);

    sphere.castShadow = true; //con esto le indicamos que queremos que emita sombra

    sphere.position.x = 20;
    sphere.position.y = 4;
    sphere.position.z = 2;
    scene.add(sphere);

    camera.position.x = -30;
    camera.position.y = 40;
    camera.position.z = 30;
    camera.lookAt(scene.position);

    var spotLight = new THREE.SpotLight(0xffffff, 0.8);
    spotLight.position.set(-40, 60, -10);
    spotLight.castShadow = true;
    scene.add(spotLight);

    $("#WebGL-salida").append(renderer.domElement);
    renderer.render(scene, camera);
  });
</script>

And please, if you know about a good beginner three.js tutorial or course (I don't care if it isn't free), tell me, because i'm a bit lost in this and like web developer i'm interested in this webGL world :)

Solution

You can improve the quality of the shadow by increasing the size (and thus the resolution) of the shadow map (See SpotLight):

var spotLight = new THREE.SpotLight(0xffffff, 0.8);
spotLight.position.set(-40, 60, -10);
spotLight.castShadow = true;
    
spotLight.shadow.mapSize.width = 2048;
spotLight.shadow.mapSize.height = 2048;

The quality can be further increased by restricting the light cone angle of the spotlight

spotLight.angle = Math.PI / 8.0;

These two enhancements together have the effect of increasing the resolution of the shadow map and decreasing the area to which the shadow map is mapped. As a result, more pixels of the shadow map are projected onto less area of the scene and the quality is improved.

See the code snippet:

var renderer, camera, scene, controls;

var init = function (){
  scene  = new THREE.Scene();
  camera = new THREE.PerspectiveCamera (45, window.innerWidth/window.innerHeight, 0.1, 1000); 
  renderer = new THREE.WebGLRenderer(); 
  controls = new THREE.OrbitControls( camera, renderer.domElement );

  var color = new THREE.Color("rgb(200, 250, 250)");
  renderer.setClearColor(new THREE.Color(color));
  renderer.setSize(window.innerWidth, window.innerHeight);

  renderer.shadowMap.enabled = true;
  renderer.shadowMap.type = THREE.PCFSoftShadowMap; // default THREE.PCFShadowMap


  var ejesAyuda = new THREE.AxesHelper(20); //son los ejes de ayuda creo
  scene.add(ejesAyuda); 

  var planeGeometry = new THREE.PlaneGeometry(60, 20);
  var planeMaterial = new THREE.MeshLambertMaterial({color: 0xcccccc});

  var plane = new THREE.Mesh(planeGeometry, planeMaterial);
  plane.receiveShadow = true;
  plane.rotation.x = -0.5*Math.PI; // -90º
  plane.position.x = 15;
  plane.position.y = 0;
  plane.position.z = 0;
  scene.add(plane);


  var cubeGeometry = new THREE.BoxGeometry( 4, 4, 4);
  var cubeMaterial = new THREE.MeshLambertMaterial({color: 0xff0000});
  var cube = new THREE.Mesh(cubeGeometry, cubeMaterial);
  cube.castShadow = true; //con esto le indicamos que queremos que emita sombra
  cube.position.x= -4;
  cube.position.y = 3;
  cube.position.z = 0;
  scene.add(cube);

  var sphereGeometry = new THREE.SphereGeometry (4, 20, 20);
  var sphereMaterial = new THREE.MeshLambertMaterial({color: 0x7777ff});
  var sphere = new THREE.Mesh (sphereGeometry, sphereMaterial);
  sphere.castShadow = true; //con esto le indicamos que queremos que emita sombra
  sphere.position.x = 20;
  sphere.position.y = 4;
  sphere.position.z = 2;
  scene.add(sphere);

  camera.position.x = -30;
  camera.position.y = 40;
  camera.position.z = 30;
  camera.lookAt(scene.position); 

  var spotLight = new THREE.SpotLight(0xffffff, 0.8);
  spotLight.position.set(-40, 60, -10);
  spotLight.castShadow = true;
  spotLight.angle = Math.PI / 8.0;
  spotLight.shadow.mapSize.width = 2048;
  spotLight.shadow.mapSize.height = 2048;
  scene.add(spotLight);

  document.getElementById("WebGL-salida").append(renderer.domElement);
  resize();
  window.onresize = resize;
};

function animate() {
    requestAnimationFrame( animate );
    renderer.render( scene, camera );
}

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

init();
animate();

<!--script src="https://threejs.org/build/three.min.js"></script-->
<!--script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script-->
<script src="https://cdn.jsdelivr.net/npm/three@0.146/build/three.js"></script>
<script src="https://cdn.jsdelivr.net/npm/three@0.146/examples/js/controls/OrbitControls.js"></script>
<div id="WebGL-salida">
</div>