What can be used to make an online code editor, with verification (similar to htmlacademy)?

Question

Code editor

Interested in what languages ​​this is implemented, and what is the approximate cost of such a miracle)

Answer 1

On any. For example it is possible on JavaScript.
As for the price, the question here is which languages ​​​​to check and what exactly to check.
For example, VS Code checks for me)))
Alas, I am not familiar with htmlacademy.