Wall-Mounted Electronics Shelf

Problem/Feature Description

A small maker studio needs a custom wall-mounted shelf unit to store Arduino boards, Raspberry Pis, and assorted components. The shelf is a rectangular enclosure like a shadow box mounted on a wall: it has a back wall, two side walls, a top and a bottom — but no panel on the face that faces outward. Inside, it has two horizontal divider shelves that split the interior into three rows, and three vertical ribs that divide each row into four bays.

The studio owner has the specifications: the internal usable space should be 200mm wide, 60mm deep, and 120mm tall, with a uniform wall thickness of 4mm. The divider shelves and ribs should use the same 4mm thickness. The unit needs four circular mounting holes (radius 2.5mm) drilled through the back wall, one near each corner of the back face.

Write a JSCAD main() function that produces this shelf unit as a single solid geometry.

Output Specification

Produce a single file named shelf.js containing the complete JSCAD script.

The script must define a main() function that returns the assembled shelf geometry. Do not produce any other files.