CODE EXAMPLE FOR JAVASCRIPT

dataform js

var form = document.forms.namedItem("fileinfo");
form.addEventListener('submit', function(ev) {

  var oOutput = document.querySelector("div"),
      oData = new FormData(form);

  oData.append("CustomField", "Données supplémentaires");

  var oReq = new XMLHttpRequest();
  oReq.open("POST", "stash.php", true);
  oReq.onload = function(oEvent) {
    if (oReq.status == 200) {
      oOutput.innerHTML = "Envoyé !";
    } else {
      oOutput.innerHTML = "Erreur " + oReq.status + " lors de la tentative d’envoi du fichier.<br />";
    }
  };

  oReq.send(oData);
  ev.preventDefault();
}, false);