On macOS i've this in my zshrc file:

`killport() { kill -9 $(lsof -t -i :$1 -sTCP:LISTEN) }`

i use it like killport 8000

Nice. I have this too. I wanted something more visual and expansive.

Yeah, I have a function `whoseport` which is just your subcommand. I usually manually type kill or whatever I want with `$(whoseport 3000)`