var xhttp = new XMLHttpRequest();
xhttp.open('POST','https://tutowebdesign.com/ajaxJson.php', true);
xhttp.send(null);
//événement load
xhttp.addEventListener("load", transferCompletejs, false);
function transferCompletejs(evt) {
  var objetJson = JSON.parse(this.response);
  document.write(objetJson.nom + " " + objetJson.prenom);
}