fetch.js

    fetch(BASE_URL, {
      method: "POST",
      headers
    })
      .then(response => response.body)
      .then(response => {
        const reader = response.getReader();
        // read() returns a promise that resolves
        // when a value has been received
        reader
          .read()
          .then(function processText({ done, value }) {
            // Result objects contain two properties:
            // done  - true if the stream has already given you all its data.
            // value - some data. Always undefined when done is true.
            if (done) {
              console.log("Stream complete");
              return;
            }
            const formatedValue = JSON.parse(toText.decode(value));
            if (formatedValue.responseCode >= 400) {
              that.setState({ sent: false, error: formatedValue.data });
            }
            that.setState({
              progress: Number(formatedValue.progress),
              progressTitle: formatedValue.title
            });
            if (that.state.progress === 100) {
              that.setState({ data: formatedValue, showProgress: false });
            }
            // Read some more, and call this function again
            return reader.read().then(processText);
          })
          .catch(err => {
            console.log("Error: ", err);
            that.setState({ sent: false, error: err });
          });
      })
      .catch(err => {
        console.log("Error: ", err);
      });