Yes, there no magic. The code is compiled and run on a server. So the flow is HTML with a textarea, the text from that gets sent via HTTP POST to the server, th

Yes, there no magic. The code is compiled and run on a server. So the flow is HTML with a textarea, the text from that gets sent via HTTP POST to the server, the server then "shells out" and lets the os run `go build` or `javac` and captures stdout and stderr. It runs the compiled program, also capturing stdout and stderr and returns all that text to the user. It can do this as a result of the original HTTP POST or you could have a like a websocket open and the results come back via that.