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;

init();
animate();

function init() {

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

    scene = new THREE.Scene();

   	var material = new THREE.MeshNormalMaterial();

    var mesh1 = new THREE.Mesh( new THREE.BoxGeometry( 0.2, 0.2, 0.2 ), material );
		mesh1.position.x = - 0.5;
		mesh1.updateMatrix();
    //scene.add( mesh1 );
		
		var mesh2 = new THREE.Mesh( new THREE.SphereGeometry( 0.2, 16, 8 ), material );
    scene.add( mesh2 );
		
		// merge
		
		mesh2.geometry.merge( mesh1.geometry, mesh1.matrix );
		

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

}

function animate() {

    requestAnimationFrame( animate );
    renderer.render( scene, camera );

}