It’s common in lots of modern tools to build shader trees using UI, this is analogous to that. It’s not really fixed function because you can make your tree/shader as big as you want and it has all of the math functions that GLSL has. Fixed function usually means something like a limited fixed set of nodes and you can turn the constant knobs.

Unless I missed it somewhere, the two nodes that seem to be missing here are an if() node and a loop() node. I’m guessing a loop() node can be done on the JavaScript side for small loops - it’d be the same as loop unrolling. For big loops or loops with unknown bounds at compile time, it’s not clear if there’s a way with TSL. You can simulate if() behavior using the nodes provided, but you can’t avoid executing both sides of the if().

It’s been a long time since I wrote a three.js shader, so I’m not sure what the “old” example is doing. It looks like it might be a little dynamic code injection to convert from a typical GLSL shader to something three.js needs.