Per Javascript feststellen, ob eine Datei existiert - ist das möglich?

[Linuchs]

var request = new XMLHttpRequest();
request.open('POST','a10.pdf', true);
if (request.status >= 200 && request.status < 300)

Da fehlt Einiges. Ich mache es so:

  request.open('post', url, true);            // Request öffnen
  request.send(null);                         // Request senden
  request.onreadystatechange = zeigeHelptext; // Request auswerten
...
function zeigeHelptext( )
{
  // http://www.w3schools.com/ajax/ajax_xmlhttprequest_onreadystatechange.asp
  // The onreadystatechange event is triggered every time the readyState changes.
  if ( request.readyState == 4 && request.status == 200 )
  {
    document.getElementById( "helptext" ).innerHTML     = request.responseText;
    document.getElementById( "helptext" ).style.display = "block";
  }
}

Info:

onreadystatechange
Stores a function (or the name of a function) to be called automatically each time the readyState property changes

readyState
Holds the status of the XMLHttpRequest. Changes from 0 to 4:
0: request not initialized
1: server connection established
2: request received
3: processing request
4: request finished and response is ready

status
200: "OK"
404: Page not found

Also warte den readyState == 4 ab und prüfe dann auf status == 200 Datei geladen oder status == 404 Datei nicht erreichbar.

Linuchs