JSFiddle - React, Tailwind, and code Playground

HTML

<form enctype="multipart/form-data" action="/echo/html" method="post" name="fileinfo" accept-charset="windows-1251">
  <label>Label:</label>
  <input type="text" name="label" size="12" maxlength="32" value="får løbende" /><br />
  <input type="submit" value="Send standart">
</form>
<button onclick="sendForm()">Send ajax!</button>

JavaScript

window.sendForm = function() {
  var oOutput = document.getElementById("output"),
     oData = new FormData(document.forms.namedItem("fileinfo"));
  var oReq = new XMLHttpRequest();
  oReq.open("POST", "/echo/html", true);
  oReq.send(oData);
}