optimizeGeometry.js

function optimizeGeometry(geometry) {
    var saveVerts = []; 

    geometry.vertices.forEach((vert, i) => {
        var present = geometry.faces.some(face => {
            return face[0] === i || face[1] === i || face[2] === i
        });

        if (present)
            saveVerts.push(i);
    });

    geometry.faces.forEach((face, i) => { // replace indices
        face[0] = saveVerts.indexOf(face[0]);
        face[1] = saveVerts.indexOf(face[1]);
        face[2] = saveVerts.indexOf(face[2]);
    })

    geometry.vertices = geometry.vertices.filter((vert, i) => { // save only used vertices
        return saveVerts.indexOf(i) !== -1;
    });
}