How to send array or dictionary in XMLHttpRequest with JS in Python?

Question

Python

Good day!
Here is the code:

document.querySelector('#rateForm').onsubmit = () => {
                      const xhr = new XMLHttpRequest();
                      var rate = document.querySelector('#rate').value;
                      var text = document.querySelector('#text').value;

                      word = {"rate": rate, "text": text, "isbn": isbn}

                      const currency = word;
                      xhr.open('POST', '/comment', true);

                      xhr.onload = () => {
                        const data = JSON.parse(xhr.responseText);

                        console.log(data)

                      }

                      const data = new FormData();
                      data.append('currency', currency);
                      console.log(currency)
                      xhr.send(data);
                      return false;

                    };

Please explain how to make a request correctly so that the data reaches the server. In this example, my server simply accepts an object, but there is no data in it.