THREE.extras.curves

//Create a closed wavey loop
const curve = new THREE.CatmullRomCurve3( [
new THREE.Vector3( -10, 0, 10 ),
new THREE.Vector3( -5, 5, 5 ),
new THREE.Vector3( 0, 0, 0 ),
new THREE.Vector3( 5, -5, 5 ),
new THREE.Vector3( 10, 0, 10 )
] );

const points = curve.getPoints( 50 );
const geometry = new THREE.BufferGeometry().setFromPoints( points );

const material = new THREE.LineBasicMaterial( { color: 0xff0000 } );

// Create the final object to add to the scene
const curveObject = new THREE.Line( geometry, material );

const curve = new THREE.EllipseCurve(
0, 0,
10, 10,
0, 2 * Math.PI,
false,
0
);

const points = curve.getPoints( 50 );
const geometry = new THREE.BufferGeometry().setFromPoints( points );

const material = new THREE.LineBasicMaterial( { color: 0xff0000 } );

// Create the final object to add to the scene
const ellipse = new THREE.Line( geometry, material );