Shapes can mirror (reflect) about the X, Y, or Z axis, and more specifically about any origin.

Learn about reflection at MathIsFun.com

Defaults:

• origin : [0, 0, 0]
• normal : [0, 0, 1] (mirror about the Z axis)

const myshape = cube({size: [5, 20, 5]})
const newshape = mirror({origin: 3, 3, 3], normal: [1, 0, 1]}, myshape)

There are simple versions of this function to mirror a single axis about the origin.

const myshape = cube({size: [5, 20, 5]})
let newshape = mirrorX(myshape)
newshape = mirrorY(newshape)
newshape = mirrorZ(newshape)