I was trying to decompose it, and I remembered that there is another function similar to setTimeout(). setTimeout() calls the function once, and then spin.js anim() function calls again each time it completes its work. The other variant calls a function repeatedly at a prescribed interval.
At first I couldn't remember the second function, so I went looking on the web. I was certain that some reference for setTimeout() would mention the other version. If there is a page that connects them though, I sure couldn't find it. Thankfully, I not only remembered that there is this other version, but I finally remembered that I had used it in one of my projects to poll the address bar, when onhashchange is not defined. The function is setInterval(). When I went back to w3 schools, it was declared in the general list of window methods, but not associated in any way with setTimeout() or anything Timer based.