That uses Pyodide. From Pyodide's own pages: "At present a first load of Pyodide requires a 6.4 MB download, and the environment initialization takes 4 to 5 s

That uses Pyodide. From Pyodide's own pages: "At present a first load of Pyodide requires a 6.4 MB download, and the environment initialization takes 4 to 5 seconds." So, yes, it works. But there's plenty of situations where a big download followed by a 5 second stall is a non-starter.