particles/test1.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        html, body {
            padding:0;
            margin:0;
        }
    </style>
    <script src="./node_modules/three/build/three.min.js"></script>
</head>
<body>

<script type="module">
    const rand = (min,max) => min + Math.random()*(max-min)


    let scene, camera, renderer
    let particles


    const MAX = 100
    function setupScene() {
        particles = new THREE.Group()
        const geo = new THREE.SphereBufferGeometry(0.1)
        const mat = new THREE.MeshLambertMaterial({color: 'red'})
        for(let i=0; i<MAX; i++) {
            const particle = new THREE.Mesh(geo,mat)
            particle.velocity = new THREE.Vector3(rand(-0.01, 0.01), 0.06, rand(-0.01, 0.01))
            particle.acceleration = new THREE.Vector3(0,-0.001,0)
            particle.position.x = rand(-1,1)
            particle.position.z = rand(-1,1)
            particle.position.y = rand(-1,-3)
            particles.add(particle)
        }
        particles.position.z = -4
        scene.add(particles)
    }

    function init() {
        //setup canvas
        const container = document.createElement( 'div' );
        document.body.appendChild( container );
        //setup scene and cameras
        scene = new THREE.Scene();
        scene.background = new THREE.Color( 0x000000 );
        camera = new THREE.PerspectiveCamera( 70, window.innerWidth / window.innerHeight, 0.1, 50 );
        //setup light
        var light = new THREE.DirectionalLight( 0xffffff, 1.0 );
        light.position.set( 0, -1, 1 ).normalize();
        scene.add( light );

        //setup renderer
        renderer = new THREE.WebGLRenderer( { antialias: true } );
        renderer.setPixelRatio( window.devicePixelRatio );
        renderer.setSize( window.innerWidth, window.innerHeight );
        container.appendChild( renderer.domElement );
        //setup events
        window.addEventListener( 'resize', ()=>{
            camera.aspect = window.innerWidth / window.innerHeight;
            camera.updateProjectionMatrix();
            renderer.setSize( window.innerWidth, window.innerHeight );
        },false);


        setupScene()
    }


    function render(time) {
        particles.children.forEach(p => {
            p.velocity.add(p.acceleration)
            p.position.add(p.velocity)
        })
        renderer.render( scene, camera );
    }

    init();
    renderer.setAnimationLoop( render );

</script>

</body>
</html>