mesh-combine 
Combine multiple indexed meshes into a single indexed mesh.
This should help constructing indexed meshes from smaller primitives without getting too bogged down in indexing everything manually.
Usage
mesh = combine(meshes)
Given an array of meshes, return a combined mesh. Each mesh in the array
should be an object with two properties:
positions: the positions in the individual mesh.cells: a list of faces in the individual mesh.
See Also
License
MIT. See LICENSE.md for details.