var xhr = null; 

function getXhr(){
  if(window.XMLHttpRequest) // Firefox et autres
    xhr = new XMLHttpRequest(); 
  else if(window.ActiveXObject){ // Internet Explorer 
    try {
      xhr = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e) {
      xhr = new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
  else { // XMLHttpRequest non supporté par le navigateur 
    alert("Votre navigateur ne supporte pas les objets XMLHTTPRequest..."); 
    xhr = false; 
  } 
}

function displayImg(which,how,where){
  getXhr();
  xhr.onreadystatechange = function(){
    if(xhr.readyState == 4 && xhr.status == 200){
      dispimg = xhr.responseText;
      document.getElementById(where).innerHTML = dispimg;
    }
  }
  xhr.open("POST","/display_item.php",true);
  xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
  xhr.send("id="+which+"&template="+how);
}