fetch - get a Vec<u8>

fetch.rs

                        let window = web_sys::window().unwrap();
                        let pr = window.fetch_with_str("https://v3-cinemeta.strem.io/catalog/movie/top.json");
                        let fut = JsFuture::from(pr)
                            .and_then(|resp_value| {
                                // @TODO: reduce number of copies
                                assert!(resp_value.is_instance_of::<Response>());
                                let resp: Response = resp_value.dyn_into().unwrap();
                                let buf_promise = resp.array_buffer().unwrap();
                                JsFuture::from(buf_promise).map(|buf_val| {
                                    assert!(buf_val.is_instance_of::<ArrayBuffer>());
                                    let typebuf: js_sys::Uint8Array = js_sys::Uint8Array::new(&buf_val);
                                    let mut body = vec![0; typebuf.length() as usize];
                                    typebuf.copy_to(&mut body[..]);
                                    body
                                })
                            })
                            .and_then(move |body| {
                                let resp: CatalogResponse = serde_json::from_slice(&body).unwrap();
                                emit(&Action::CatalogReceived(Ok(resp)));
                                future::ok(())
                            })
                            .map_err(|_| ());
                        spawn_local(fut)