* JavaScript

  ```js
  export default {
    async fetch(req) {
      const data =
        req.cf !== undefined
          ? req.cf
          : { error: "The `cf` object is not available inside the preview." };


      return new Response(JSON.stringify(data, null, 2), {
        headers: {
          "content-type": "application/json;charset=UTF-8",
        },
      });
    },
  };
  ```

* TypeScript

  ```ts
  export default {
    async fetch(req): Promise<Response> {
      const data =
        req.cf !== undefined
          ? req.cf
          : { error: "The `cf` object is not available inside the preview." };


      return new Response(JSON.stringify(data, null, 2), {
        headers: {
          "content-type": "application/json;charset=UTF-8",
        },
      });
    },
  } satisfies ExportedHandler;
  ```

* Python

  ```py
  import json
  from workers import Response
  from js import JSON


  def on_fetch(request):
      error = json.dumps({ "error": "The `cf` object is not available inside the preview." })
      data = request.cf if request.cf is not None else error
      headers = {"content-type":"application/json"}
      return Response(JSON.stringify(data, None, 2), headers=headers)
  ```
