Placing a random vector on a sphere or between two spheres that share a (0,0,0) center (JavaScript and THREE.js)

randomVectorBetweenSpheres.js

/*
randomVectorBetweenSpheres(radius: Number, depth: Number) -> THREE.Vector3
@param radius <Number>: Radius of inner sphere (distance between center of sphere and closest possible random vector)
@param depth <Number>: Distance between inner sphere and outer sphere (radius+depth = furthest possible random vector)
*/
function randomVectorBetweenSpheres(radius, depth) {
  // Create random radius between radius and radius+depth
  const randomRadius = Math.floor(Math.random() * (radius + depth - radius + 1) + radius);
  // Return random vector on sphere with random radius
  return this.randomSphereSurfaceVector(randomRadius);
},

/*
randomSphereSurfaceVector(radius: Number) -> THREE.Vector3
@param radius <Number>: Radius of sphere on which to put a random vector
*/
function randomSphereSurfaceVector(radius) {
  const theta = 2 * Math.PI * Math.random();
  const phi = Math.acos(2 * Math.random() - 1);
  const x = radius * Math.sin(phi) * Math.cos(theta);
  const y = radius * Math.sin(phi) * Math.sin(theta);
  const z = radius * Math.cos(phi);
  return new THREE.Vector3(x, y, z);
}