for @react_or.js

const send = (file) => {
  const xhr = new XMLHttpRequest();
  const formData = new FormData();

  formData.append("avatar", file);
  xhr.open("POST", "/", true);

  xhr.upload.onprogress = function(event) {
    if (event.lengthComputable) {
      const percent = (event.loaded / event.total) * 100;

      document.getElementById("output").innerText = percent + "%";
    }
  };

  xhr.send(formData);
};

const click = () => {
  const file = document.getElementById("file").files[0];

  send(file);
};

document.getElementById("btn").addEventListener("click", click);