1. /* @pjs preload="box.obj"; */
2. PShape s;
3. void setup() {
4.   size(700, 700, P3D);
5.   s = loadShape("box.obj");
6. }
7. 
   
8. void draw() {
9.   background(0);
10.   lights();
11.   shape(s, 0, 0);
12. }

I have copied "box.obj" into the "web-export" folder for it to be found by the preload method.

I get this error though:

Resource interpreted as Image but transferred with MIME type text/plain: http://127.0.0.1:62818/box.obj.