The programming language is three.js but not using the THREE.CylinderGeometry that it is in the page of three.js.

Write an analogous function that generates and returns the geometry of a cylinder. The function createCylinder(n, rad, len) returns the geometry of an n-sided cylinder of radius rad. It should be centered at the origin and aligned with the y-axis, so that the cylinder's top face lies in the plane y = len/2 and its bottom face in the plane y=-len/2. Do not use THREE.CylinderGeometry