Upload file on textarea drop

upload.js

function addImageMarkdown(e, altText, imagePath) {
  var startPos = e.selectionStart;
  var endPos = e.selectionEnd;
  e.value = e.value.substring(0, startPos)
  + "![" + altText + "](" + imagePath + ")"
  + e.value.substring(endPos, e.value.length);
}

$(document).on('drop', 'textarea', function(e) {
  e.preventDefault();
  var dt = e.originalEvent.dataTransfer;
  var f = dt.files[0];

  t = e.currentTarget;
  // Adds markdown for image to textarea at cursor position.
  addImageMarkdown(t, f.name, " ... ");

  var fd = new FormData();
  fd.append("file", f);

  var request = new XMLHttpRequest();
  request.open("POST", "/upload");
  request.onloadend = function(e) {
    // The response is the path to the file on the server.
    var resp = e.currentTarget.response;
    // Update the text with the correct path for the image.
    t.value = t.value.replace(/\.\.\./, resp.slice(1));
    $(t).keyup();
  };
  request.send(fd);
});