Does that example work for you. I copy it and trying to run it to see it work and it giving me errror

✘ [ERROR] Expected ")" but found ":"

    src/index.js:4:23:
      4 │     async fetch(request: Request, env: Env): Promise<Response> {
        │                        ^
        ╵                        )


✘ [ERROR] Expected ")" but found ":"

    src/index.js:4:23:
      4 │     async fetch(request: Request, env: Env): Promise<Response> {
        │                        ^
        ╵                        )

So before I try anything wanted to see if it worked for your or someone else.