Server Sent Event with fetch stream

fetchStream.js

const url = 'https://api.example.com/v1/sse';
const accessToken = 'test';
fetch(url, {
    headers: {
      Authorization: `Bearer ${accessToken}`,
    },
  })
  .then(response => {
    if (response.ok && response.body) {
      reader = response.body.pipeThrough(new TextDecoderStream()).getReader();

      const readStream = () =>
        reader.read().then(({
          value,
          done
        }) => {
          if (done) {
            reader.cancel();
            return Promise.resolve();
          }

          // parse the data
          const data = /{.*}/.exec(value);
          if (!data || !data[0]) {
            return readStream();
          }

          const res = JSON.parse(data[0]);

          // do something if success
          // and cancel the stream 
          // reader.cancel().catch(() => null);

          return readStream();
        });
      return readStream();
    } else {
      return Promise.reject(response);
    }
  })