Get Post Data Payload From Sent XHR

Question

I am writing some code to intercept and log ever XHR request sent over JavaScript, but I am unable to find where to access the request payload from. Is this possible to do? My code is below, this logs the url, method, and response, but no payload.

let oldXHROpen = window.XMLHttpRequest.prototype.open;
window.XMLHttpRequest.prototype.open = function (
  method,
  url,
  async,
  user,
  password
) {
  console.log("---hooked request---");
  console.log({ url });
  console.log({ method });
  console.log(this);

  this.addEventListener("load", function () {
    console.log("load: " + this.responseText);
  });

  return oldXHROpen.apply(this, arguments);
};