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I have an <iframe> that other sites can include so their users can POST a form back to my site. I'd like to handle gracefully the cases where my site is down or my server can't serve the <iframe> contents (that is, a response timeout or a 4xx or 5xx error). I tried adding an onError to the <iframe> object, but that didn't seem to do anything:

showIFrame = function() {
  var iframe = document.createElement('iframe');
  iframe.id = 'myIFrame';
  iframe.src = 'http://myserver.com/someURLThatFailsToLoad';
  iframe.onError = iframe.onerror = myHandler;
  document.body.appendChild(iframe);
myHandler = function(error) {
  document.getElementById('myIFrame').style.display = 'none';
  console.error('Error loading iframe contents: ' + error);
  return true;
If my server returns a 404 I just get the contents of the not-found page in my <iframe>. In fact, that error handler isn't ever triggered. Is there a way to make this work?
(I'm currently testing in Chrome, but I'd like it to also work for FF and IE >= 7.)
To detect whether your server is down or not, you can include an empty script file from your own domain. When the server is down, the onerror event handler will fire:
var el = document.createElement('script');
el.onerror = errorFunction;
el.src = "somebogusscript.js?" + new Date().getTime();
document.body.appendChild(el);
Note: don't forget to add a random string to the src attribute to avoid the client using a cached version (which could stop a look at the server at all).
                sorry - great point, though I had already accounted for this. See the update: iframe.onError = iframe.onerror = myHandler;
– James A. Rosen
                Sep 13, 2010 at 23:19
                Most browsers do not allow XHR requests cross-domain. This is Javascript that I provide to other sites. Indeed, the cross-domain restrictions of XHR HTTP are exactly why I'm using an <iframe> at all here.
– James A. Rosen
                Sep 13, 2010 at 23:36
                @MarcelKorpel True enough.  What I meant is the iframe element appears not to honor the onerror callback, at least in Chrome.
– jsleuth
                May 29, 2015 at 16:38
Perhaps you could try onErrorUpdate for the event handler? I couldn't see an onError handler for iFrames. If that doesn't work, you could try onLoad and then check the source of the iframe or the title of it for a 404 message.
Such as:
if (frameDoc.title == 'title the server sends for 404') {
Source:
http://bytes.com/topic/javascript/answers/166288-catch-404-when-using-iframe
iFrame Methods: http://www.java2s.com/Code/HTMLCSSReference/HTML-Tag-Reference/iframeJavaScriptMethods.htm
iFrame Properties: http://www.java2s.com/Code/HTMLCSSReference/HTML-Tag-Reference/iframeJavaScriptProperties.htm
                This could work for the 404 case, but I'm really concerned with the case where the request times out -- that is, when my servers go down.
– James A. Rosen
                Sep 13, 2010 at 23:41
                Would onTimeError trigger in that case? I think that may only work in IE though which is a shame.
– Joel Kennedy
                Sep 14, 2010 at 0:03
        
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