HTML:
<body onload="obtenirVariables()">
// this div is working, showing the sensor
 <div id="sensor0"></div>
 <form>
// I want show inside the form but is not working.
<input id="sensor0" type="text" name="S0max" maxlength="4" size="4">
<input name='BT01' type='submit' value="Send">
 </form>
</body>


javascript:
function obtenirVariables(){
var uniqueURL = "/reqEtatVariables" + "?aleatoire=" + Math.trunc(Math.random() * 1000000);
var request = new XMLHttpRequest(); // http://www.toutjavascript.com/reference/ref-xmlhttprequest.php
    request.onreadystatechange = function()
    {
     if (request.readyState == 4) {
      if (request.status == 200) {
document.getElementById("sensor0").innerHTML = this.responseXML.getElementsByTagName('sensor0')[0].childNodes[0].nodeValue;
  }
  }
 }
}

XML function

void handleXML(){
  XML="<?xml version='1.0'?>";
  XML+="<xml>";
  XML+="<pumpstate>";
  XML+= pumpstate;
  XML+="</pumpstate>";
  XML+="</xml>";
 server.send(200,"text/xml",XML);
}

server.on("/reqEtatVariables",handleXML);