Have you considered Skulpt? It’s what Anvil uses under the hood. The Skulpt website has a simple example that gets you going with an interactive textarea pretty quickly. I’ve included it as a custom component in this Anvil app.
https://anvil.works/ide#clone:NY4M3I6V4JFHCVXM=QN7ZVKEUOJWNU4HV6NLSK6BT
