upload_a_file_on_the_server.js

const files = event.dataTransfer ? event.dataTransfer.files : event.target.files;
const fileToUpload = files[0];

let xhr = new XMLHttpRequest(),
formData = new FormData();
formData.append("test", fileToUpload, fileToUpload.name);

xhr.onreadystatechange = () => {
  if(xhr.readyState == 4) {
    if(xhr.status >= 200 && xhr.status < 300)
      console.log("Success", {xhr, fileToUpload})
    else
      console.log("Error", {xhr, fileToUpload})
  }
};

xhr.open('POST', nameOfURL, true);

xhr.send(formData);