Yes, if you dig around V8 performance profiles you'll see some massive "Optimizing Code" blocks that appear at the bottom of a frequently-hit routine once, then subsequent calls to that same routine will run faster.

That being said, while I haven't investigated this super thoroughly, in my experience the delta is usually small.

Trying again with timers internal to the code (previously used `time node ray.js`), initial go is 190ms, then 170ms, 160ms, and after that hovers around 140-150ms for the remaining 97 runs.

If I remove the FS operations it's instead 160ms initially, then drops to 130ms by the third go and hovers around there.

Thanks! Does this include the time to actually write the image data to the filesystem, or just append it to an internal buffer that will be eventually written?

Yes, V8 doing JIT optimization is why the modern web exists. Before V8 JS was slow so you only used it when you had to.