Develop Reference

Detect when an iframe is loaded

I'm using an <iframe> (I know, I know, ...) in my app (single-page application with ExtJS 4.2) to do file downloads because they contain lots of data and can take a while to generate the Excel file (we're talking anything from 20 seconds to 20 minutes depending on the parameters).
The current state of things is : when the user clicks the download button, he is "redirected" by Javascript (window.location.href = xxx) to the page doing the export, but since it's done in PHP, and no headers are sent, the browser continuously loads the page, until the file is downloaded. But it's not very user-friendly, because nothing shows him whether it's still loading, done (except the file download), or failed (which causes the page to actually redirect, potentially making him lose the work he was doing).
So I created a small non-modal window docked in the bottom right corner that contains the iframe as well as a small message to reassure the user. What I need is to be able to detect when it's loaded and be able to differenciate 2 cases :
No data : OK => Close window
Text data : Error message => Display message to user + Close window
But I tried all 4 events (W3Schools doc) and none is ever fired. I could at least understand that if it's not HTML data returned, it may not be able to fire the event, but even if I force an error to return text data, it's not fired.
If anyone know of a solution for this, or an alternative system that may fit here, I'm all ears ! Thanks !
EDIT : Added iframe code. The idea is to get a better way to close it than a setTimeout.
var url = 'http://mywebsite.com/my_export_route';
var ifr = $('<iframe class="dl-frame" src="'+url+'" width="0" height="0" frameborder="0"></iframe>');
ifr.appendTo($('body'));
setTimeout(function() {
$('.dl-frame').remove();
}, 3000);

I wonder if it would require some significant changes in both frontend and backend code, but have you considered using AJAX? The workflow would be something like this: user sends AJAX request to start file generating and frontend constantly polls it's status from the server, when it's done - show a download link to the user. I believe that workflow would be more straightforward.
Well, you could also try this trick. In parent window create a callback function for the iframe's complete loading myOnLoadCallback, then call it from the iframe with parent.myOnLoadCallback(). But you would still have to use setTimeout to handle server errors/connection timeouts.
And one last thing - how did you tried to catch iframe's events? Maybe it something browser-related. Have you tried setting event callbacks in HTML attributes directly? Like
<iframe onload="done()" onerror="fail()"></iframe>
That's a bad practice, I know, but sometimes job need to be done fast, eh?
UPDATE
Well, I'm afraid you have to spend a long and painful day with a JS debugger. load event should work. I still have some suggestions, though:
1) Try to set event listener before setting element's src. Maybe onload event fires so fast that it slips between creating element and setting event's callback
2) At the same time try to check if your server code plays nicely with iframes. I have made a simple test which attempts to download a PDF from Dropbox, try to replace my URL with your backed route's.
<script src="https://code.jquery.com/jquery-1.11.1.min.js"></script>
<iframe id="book"></iframe>
<button id="go">Request downloads!</button>
<script>
var bookUrl = 'https://www.dropbox.com/s/j4o7tw09lwncqa6/thinkpython.pdf';
$('#book').on('load', function(){
console.log('WOOT!', arguments);
});
$('#go').on('click', function(){
$('#book').attr('src', bookUrl);
});
</script>
UPDATE 2
3) Also, look at the Network tab of your browser's debugger, what happens when you set src to the iframe, it should show request and server's response with headers.

I've tried with jQuery and it worked just fine as you can see in this post.
I made a working example here.
It's basically this:
<iframe src="http://www.example.com" id="myFrame"></iframe>
And the code:
function test() {
alert('iframe loaded');
}
$('#myFrame').load(test);
Tested on IE11.

I guess I'll give a more hacky alternative to the more proper ways of doing it that the others have posted. If you have control over the PHP download script, perhaps you can just simply output javascript when the download is complete. Or perhaps redirect to a html page that runs javascript. The javascript run, can then try to call something in the parent frame. What will work depends if your app runs in the same domain or not
Same domain
Same domain frame can just use frame javascript objects to reference each other. so it could be something like, in your single page application you can have something like
window.downloadHasFinished=function(str){ //Global pollution. More unique name?
//code to be run when download has finished
}
And for your download php script, you can have it output this html+javascript when it's done
<script>
if(parent && parent.downloadHasFinished)
parent.downloadHasFinished("if you want to pass a data. maybe export url?")
</script>
Demo jsfiddle (Must run in fullscreen as the frames have different domain)
Parent jsfiddle
Child jsfiddle
Different Domains
For different domains, We can use postMessage. So in your single page application it will be something like
$(window).on("message",function(e){
var e=e.originalEvent
if(e.origin=="http://downloadphp.anotherdomain.com"){ //for security
var message=e.data //data passed if any
//code to be run when download has finished
}
});
and in your php download script you can have it output this html+javascript
<script>
parent.postMessage("if you want to pass data",
"http://downloadphp.anotherdomain.com");
</script>
Parent Demo
Child jsfiddle
Conclusion
Honestly, if the other answers work, you should probably use those. I just thought this was an interesting alternative so I posted it up.

You can use the following script. It comes from a project of mine.
$("#reportContent").html("<iframe id='reportFrame' sandbox='allow-same-origin allow-scripts' width='100%' height='300' scrolling='yes' onload='onReportFrameLoad();'\></iframe>");

Maybe you should use
$($('.dl-frame')[0].contentWindow.document).ready(function () {...})

Try this (pattern)
$(function () {
var session = function (url, filename) {
// `url` : URL of resource
// `filename` : `filename` for resource (optional)
var iframe = $("<iframe>", {
"class": "dl-frame",
"width": "150px",
"height": "150px",
"target": "_top"
})
// `iframe` `load` `event`
.one("load", function (e) {
$(e.target)
.contents()
.find("html")
.html("<html><body><div>"
+ $(e.target)[0].nodeName
+ " loaded" + "</div><br /></body></html>");
alert($(e.target)[0].nodeName
+ " loaded" + "\nClick link to download file");
return false
});
var _session = $.when($(iframe).appendTo("body"));
_session.then(function (data) {
var link = $("<a>", {
"id": "file",
"target": "_top",
"tabindex": "1",
"href": url,
"download": url,
"html": "Click to start {filename} download"
});
$(data)
.contents()
.find("body")
.append($(link))
.addBack()
.find("#file")
.attr("download", function (_, o) {
return (filename || o)
})
.html(function (_, o) {
return o.replace(/{filename}/,
(filename || $(this).attr("download")))
})
});
_session.always(function (data) {
$(data)
.contents()
.find("a#file")
.focus()
// start 6 second `download` `session`,
// on `link` `click`
.one("click", function (e) {
var timer = 6;
var t = setInterval(function () {
$(data)
.contents()
.find("div")
// `session` notifications
.html("Download session started at "
+ new Date() + "\n" + --timer);
}, 1000);
setTimeout(function () {
clearInterval(t);
$(data).replaceWith("<span class=session-notification>"
+ "Download session complete at\n"
+ new Date()
+ "</span><br class=session-notification />"
+ "<a class=session-restart href=#>"
+ "Restart download session</a>");
if ($("body *").is(".session-restart")) {
// start new `session`,
// on `.session-restart` `click`
$(".session-restart")
.on("click", function () {
$(".session-restart, .session-notification")
.remove()
// restart `session` (optional),
// or, other `session` `complete` `callback`
&& session(url, filename ? filename : null)
})
};
}, 6000);
});
});
};
// usage
session("http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf", "ECMA_JS.pdf")
});
jsfiddle http://jsfiddle.net/guest271314/frc82/

In regards to your comment about to get a better way to close it instead of setTimeout. You could use jQuery fadeOut option or any of the transitions and in the 'complete' callback remove the element. Below is an example you can dump right into a fiddle and only need to reference jQuery.
I also wrapped inside listener for 'load' event to not do the fade until the iFrame has been loaded as question originally was asking.
// plugin your URL here
var url = 'http://jquery.com';
// create the iFrame, set attrs, and append to body
var ifr = $("<iframe>")
.attr({
"src": url,
"width": 300,
"height": 100,
"frameborder": 0
})
.addClass("dl-frame")
.appendTo($('body'))
;
// log to show its part of DOM
console.log($(".dl-frame").length + " items found");
// create listener for load
ifr.one('load', function() {
console.log('iframe is loaded');
// call $ fadeOut to fade the iframe
ifr.fadeOut(3000, function() {
// remove iframe when fadeout is complete
ifr.remove();
// log after, should no longer exist in DOM
console.log($(".dl-frame").length + " items found");
});
});

If you are doing a file download from a iframe the load event wont fire :) I was doing this a week ago. The only solution to this problem is to call a download proxy script with a tag and then return that tag trough a cookie then the file is loaded. min while yo need to have a setInterval on the page witch will watch for that specific cookie.
// Jst to clearyfy
var token = new Date().getTime(); // ticks
$('<iframe>',{src:"yourproxy?file=somefile.file&token="+token}).appendTo('body');
var timers = [];
timers[timers.length+1] = setInterval(function(){
var _index = timers.length+1;
var cookie = $.cooke(token);
if(typeof cookie != "undefined"){
// File has been downloaded
$.removeCookie(token);
clearInterval(_index);
}
},400);
in your proxy script add the cookie with the name set to the string sent bay the token url parameter.

If you control the script in server that generates excel or whatever you are sending to iframe why don't you put a UID flag and store it in session with value 0, so... when iframe is created and server script is called just set UID flag to 1 and when script is finished (the iframe will be loaded) just put it to 2.
Then you only need a timer and a periodic AJAX call to the server to check the UID flag... if it's set to 0 the process doesn't started, if it's 1 the file is creating, and finally if it's 2 the process has been ended.
What do you think? If you need more information about this approach just ask.

What you are saying could be done for images and other media formats using $(iframe).load(function() {...});
For PDF files or other rich media, you can use the following Library:
http://johnculviner.com/jquery-file-download-plugin-for-ajax-like-feature-rich-file-downloads/
Note: You will need JQuery UI

You can use this library. The code snippet for you purpose would be something like:
window.onload = function () {
rajax_obj = new Rajax('',
{
action : 'http://mywebsite.com/my_export_route',
onComplete : function(response) {
//This will only called if you have returned any response
// instead of file from your export script
// In your case 2
// Text data : Error message => Display message to user
}
});
}
Then you can call rajax_obj.post() on your download link click.
Download
NB: You should add some header to your PHP script so it force file download
header('Content-Disposition: attachment; filename="'.$file.'"');
header('Content-Transfer-Encoding: binary');

There is two solutions that i can think of. Either you have PHP post it's progress to a MySQL table where from frontend will be pulling information from using AJAX calls to check up on the progress of the generation. Using somekind of unique key that is being generated when accessing the page would be ideal for multiple people generating excel files at the same time.
Another solution would be to use nodejs & then in PHP post the progress of the excel file using cURL or a socket to a nodejs service. Then when receiving updates from PHP in nodejs you simply write the progress of the excel file for the right socket. This will cut off some browser support though. Unless you go through with it using external libraries to bring websocket support for pretty much all browsers & versions.
Hope this answer helped. I was having the same issue previous year. Ended up doing AJAX polling having PHP post progress on the fly.

Try this:
Note: You should be on the same domain.
var url = 'http://mywebsite.com/my_export_route',
iFrameElem = $('body')
.append('<iframe class="dl-frame" src="' + url + '" width="0" height="0" frameborder="0"></iframe>')
.find('.dl-frame').get(0),
iDoc = iFrameElem.contentDocument || iFrameElem.contentWindow.document;
$(iDoc).ready(function (event) {
console.log('iframe ready!');
// do stuff here
});

Navigating / scraping hashbang links with javascript (phantomjs)

I'm trying to download the HTML of a website that is almost entirely generated by JavaScript. So, I need to simulate browser access and have been playing around with PhantomJS. Problem is, the site uses hashbang URLs and I can't seem to get PhantomJS to process the hashbang -- it just keeps calling up the homepage.
The site is http://www.regulations.gov. The default takes you to #!home. I've tried using the following code (from here) to try and process different hashbangs.
if (phantom.state.length === 0) {
if (phantom.args.length === 0) {
console.log('Usage: loadreg_1.js <some hash>');
phantom.exit();
}
var address = 'http://www.regulations.gov/';
console.log(address);
phantom.state = Date.now().toString();
phantom.open(address);
} else {
var hash = phantom.args[0];
document.location = hash;
console.log(document.location.hash);
var elapsed = Date.now() - new Date().setTime(phantom.state);
if (phantom.loadStatus === 'success') {
if (!first_time) {
var first_time = true;
if (!document.addEventListener) {
console.log('Not SUPPORTED!');
}
phantom.render('result.png');
var markup = document.documentElement.innerHTML;
console.log(markup);
phantom.exit();
}
} else {
console.log('FAIL to load the address');
phantom.exit();
}
}
This code produces the correct hashbang (for instance, I can set the hash to '#!contactus') but it doesn't dynamically generate any different HTML--just the default page. It does, however, correctly output that has when I call document.location.hash.
I've also tried to set the initial address to the hashbang, but then the script just hangs and doesn't do anything. For example, if I set the url to http://www.regulations.gov/#!searchResults;rpp=10;po=0 the script just hangs after printing the address to the terminal and nothing ever happens.

The issue here is that the content of the page loads asynchronously, but you're expecting it to be available as soon as the page is loaded.
In order to scrape a page that loads content asynchronously, you need to wait to scrape until the content you're interested in has been loaded. Depending on the page, there might be different ways of checking, but the easiest is just to check at regular intervals for something you expect to see, until you find it.
The trick here is figuring out what to look for - you need something that won't be present on the page until your desired content has been loaded. In this case, the easiest option I found for top-level pages is to manually input the H1 tags you expect to see on each page, keying them to the hash:
var titleMap = {
'#!contactUs': 'Contact Us',
'#!aboutUs': 'About Us'
// etc for the other pages
};
Then in your success block, you can set a recurring timeout to look for the title you want in an h1 tag. When it shows up, you know you can render the page:
if (phantom.loadStatus === 'success') {
// set a recurring timeout for 300 milliseconds
var timeoutId = window.setInterval(function () {
// check for title element you expect to see
var h1s = document.querySelectorAll('h1');
if (h1s) {
// h1s is a node list, not an array, hence the
// weird syntax here
Array.prototype.forEach.call(h1s, function(h1) {
if (h1.textContent.trim() === titleMap[hash]) {
// we found it!
console.log('Found H1: ' + h1.textContent.trim());
phantom.render('result.png');
console.log("Rendered image.");
// stop the cycle
window.clearInterval(timeoutId);
phantom.exit();
}
});
console.log('Found H1 tags, but not ' + titleMap[hash]);
}
console.log('No H1 tags found.');
}, 300);
}
The above code works for me. But it won't work if you need to scrape search results - you'll need to figure out an identifying element or bit of text that you can look for without having to know the title ahead of time.
Edit: Also, it looks like the newest version of PhantomJS now triggers an onResourceReceived event when it gets new data. I haven't looked into this, but you might be able to bind a listener to this event to achieve the same effect.

Timing out tracking pixels in webkit browsers

I have a javascript that creates several div elements and inside them an img tag for each of several image urls. I also have a timeout function that after a period is supposed to cause the image to stop loading. In FF this can be achieved by setting the img tag's src attribute to be blank. In webkit browsers it's a different story since all requests are made asynchronously.
The code I have so far looks similar to this:
function tag(url_array, timeout)
{
var _tag_div = document.getElementById('tag_div');
for(var i in url_array)
{
var e = document.createElement('div');
e.setAttribute('id', '_tag_' + i);
e.innerHTML = '<img src="' + urls[i] + '"/>';
_tag_div.appendChild(e);
setTimeout(blank_img.bind(window, i), timeout);
}
function blank_img(x)
{
document.getElementById('_tag_' + x).firstChild.src = '';
}
}
As I said this works well in FF but in webkit browsers it does nothing to stop the loading of the images. Given that this is going to be used for a pixel tracking system on 3rd party pages the code needs to be as lightweight as possible. Does anybody know of a solution to this problem or can maybe assist me in finding one? Thanks in advance,
-CarbonX

Try removing them from the DOM completely with removeChild, e.g.:
function blank_img(x) {
var imgTag = document.getElementById('_tag_' + x);
if(imgTag) { imgTag.parentNode.removeChild(imgTag); }
}
I'm assuming you don't need the tags later...

Getting functions from another script in JS

I load this JS code from a bookmarklet:
function in_array(a, b)
{
for (i in b)
if (b[i] == a)
return true;
return false;
}
function include_dom(script_filename) {
var html_doc = document.getElementsByTagName('head').item(0);
var js = document.createElement('script');
js.setAttribute('language', 'javascript');
js.setAttribute('type', 'text/javascript');
js.setAttribute('src', script_filename);
html_doc.appendChild(js);
return false;
}
var itemname = '';
var currency = '';
var price = '';
var supported = new Array('www.amazon.com');
var domain = document.domain;
if (in_array(domain, supported))
{
include_dom('http://localhost/bklts/parse/'+domain+'.js');
alert(getName());
}
[...]
Note that the 'getName()' function is in http://localhost/bklts/parse/www.amazon.com/js. This code works only the -second- time I click the bookmarklet (the function doesn't seem to get loaded until after the alert()).
Oddly enough, if I change the code to:
if (in_array(domain, supported))
{
include_dom('http://localhost/bklts/parse/'+domain+'.js');
alert('hello there');
alert(getName());
}
I get both alerts on the first click, and the rest of the script functions. How can I make the script work on the first click of the bookmarklet without spurious alerts?
Thanks!
-Mala

Adding a <script> tag through DHTML makes the script load asynchroneously, which means that the browser will start loading it, but won't wait for it to run the rest of script.
You can handle events on the tag object to find out when the script is loaded. Here is a piece of sample code I use that seems to work fine in all browsers, although I'm sure theres a better way of achieving this, I hope this should point you in the right direction:
Don't forget to change tag to your object holding the <script> element, fnLoader to a function to call when the script is loaded, and fnError to a function to call if loading the script fails.
Bear in mind that those function will be called at a later time, so they (like tag) must be available then (a closure would take care of that normally).
tag.onload = fnLoader;
tag.onerror = fnError;
tag.onreadystatechange = function() {
if (!window.opera && typeof tag.readyState == "string"){
/* Disgusting IE fix */
if (tag.readyState == "complete" || tag.readyState == "loaded") {
fnLoader();
} else if (tag.readyState != "loading") {
fnError();
};
} else if (tag.readyState == 4) {
if (tag.status != 200) {
fnLoader();
}
else {
fnError();
};
};
});

It sounds like the loading of the external script (http://localhost/bklts/parse/www.amazon.com/js) isn't blocking execution until it is loaded. A simple timeout might be enough to give the browser a chance to update the DOM and then immediately queue up the execution of your next block of logic:
//...
if (in_array(domain, supported))
{
include_dom('http://localhost/bklts/parse/'+domain+'.js');
setTimeout(function() {
alert(getName());
}, 0);
}
//...
In my experience, if zero doesn't work for the timeout amount, then you have a real race condition. Making the timeout longer (e.g. 10-100) may fix it for some situations but you get into a risky situation if you need this to always work. If zero works for you, then it should be pretty solid. If not, then you may need to push more (all?) of your remaining code to be executed into the external script.

The best way I could get working: Don't.
Since I was calling the JS from a small loader bookmarklet anyway (which just tacks the script on to the page you're looking at) I modified the bookmarklet to point the src to a php script which outputs the JS code, taking the document.domain as a parameter. As such, I just used php to include the external code.
Hope that helps someone. Since it's not really an answer to my question, I won't mark this as the accepted answer. If someone has a better way, I'd love to know it, but I'll be leaving my code as is:
bookmarklet:
javascript:(function(){document.body.appendChild(document.createElement('script')).src='http://localhost/bklts/div.php?d='+escape(document.domain);})();
localhost/bklts/div.php:
<?php
print("
// JS code
");
$supported = array("www.amazon.com", "www.amazon.co.uk");
$domain = #$_GET['d']
if (in_array($domain, $supported))
include("parse/$domain.js");
print("
// more JS code
");
?>

Detect failure to load contents of an iframe

I can detect when the content of an iframe has loaded using the load event. Unfortunately, for my purposes, there are two problems with this:
If there is an error loading the page (404/500, etc), the load event is never fired.
If some images or other dependencies failed to load, the load event is fired as usual.
Is there some way I can reliably determine if either of the above errors occurred?
I'm writing a semi-web semi-desktop application based on Mozilla/XULRunner, so solutions that only work in Mozilla are welcome.

If you have control over the iframe page (and the pages are on the same domain name), a strategy could be as follows:
In the parent document, initialize a variable var iFrameLoaded = false;
When the iframe document is loaded, set this variable in the parent to true calling from the iframe document a parent's function (setIFrameLoaded(); for example).
check the iFrameLoaded flag using the timer object (set the timer to your preferred timeout limit) - if the flag is still false you can tell that the iframe was not regularly loaded.
I hope this helps.

This is a very late answer, but I will leave it to someone who needs it.
Task: load iframe cross-origin content, emit onLoaded on success and onError on load error.
This is the most cross browsers origin independent solution I could develop. But first of all I will briefly tell about other approaches I had and why they are bad.
1. iframe That was a little shock for me, that iframe only has onload event and it is called on load and on error, no way to know it is error or not.
2. performance.getEntriesByType('resource'). This method returns loaded resources. Sounds like what we need. But what a shame, firefox always adds Resource in resources array no matter it is loaded or failed. No way to know by Resource instance was it success. As usual. By the way, this method does not work in ios<11.
3. script I tried to load html using <script> tag. Emits onload and onerror correctly, sadly, only in Chrome.
And when I was ready to give up, my elder collegue told me about html4 tag <object>. It is like <iframe> tag except it has fallbacks when content is not loaded. That sounds like what we are need! Sadly it is not as easy as it sounds.
CODE SECTION
var obj = document.createElement('object');
// we need to specify a callback (i will mention why later)
obj.innerHTML = '<div style="height:5px"><div/>'; // fallback
obj.style.display = 'block'; // so height=5px will work
obj.style.visibility = 'hidden'; // to hide before loaded
obj.data = src;
After this we can set some attributes to <object> like we'd wanted to do with iframe. The only difference, we should use <params>, not attributes, but their names and values are identical.
for (var prop in params) {
if (params.hasOwnProperty(prop)) {
var param = document.createElement('param');
param.name = prop;
param.value = params[prop];
obj.appendChild(param);
}
}
Now, the hard part. Like many same-like elements, <object> doesn't have specs for callbacks, so each browser behaves differently.
Chrome. On error and on load emits load event.
Firefox. Emits load and error correctly.
Safari. Emits nothing....
Seems like no different from iframe, getEntriesByType, script....
But, we have native browser fallback! So, because we set fallback (innerHtml) directly, we can tell if <object> is loaded or not
function isReallyLoaded(obj) {
return obj.offsetHeight !== 5; // fallback height
}
/**
* Chrome calls always, Firefox on load
*/
obj.onload = function() {
isReallyLoaded(obj) ? onLoaded() : onError();
};
/**
* Firefox on error
*/
obj.onerror = function() {
onError();
};
But what to do with Safari? Good old setTimeout.
var interval = function() {
if (isLoaded) { // some flag
return;
}
if (hasResult(obj)) {
if (isReallyLoaded(obj)) {
onLoaded();
} else {
onError();
}
}
setTimeout(interval, 100);
};
function hasResult(obj) {
return obj.offsetHeight > 0;
}
Yeah.... not so fast. The thing is, <object> when fails has unmentioned in specs behaviour:
Trying to load (size=0)
Fails (size = any) really
Fallback (size = as in innnerHtml)
So, code needs a little enhancement
var interval = function() {
if (isLoaded) { // some flag
return;
}
if (hasResult(obj)) {
if (isReallyLoaded(obj)) {
interval.count++;
// needs less then 400ms to fallback
interval.count > 4 && onLoadedResult(obj, onLoaded);
} else {
onErrorResult(obj, onError);
}
}
setTimeout(interval, 100);
};
interval.count = 0;
setTimeout(interval, 100);
Well, and to start loading
document.body.appendChild(obj);
That is all. I tried to explain code in every detail, so it may look not so foolish.
P.S. WebDev sucks

I had this problem recently and had to resort to setting up a Javascript Polling action on the Parent Page (that contains the IFRAME tag). This JavaScript function checks the IFRAME's contents for explicit elements that should only exist in a GOOD response. This assumes of course that you don't have to deal with violating the "same origin policy."
Instead of checking for all possible errors which might be generated from the many different network resources.. I simply checked for the one constant positive Element(s) that I know should be in a good response.
After a pre-determined time and/or # of failed attempts to detect the expected Element(s), the JavaScript modifies the IFRAME's SRC attribute (to request from my Servlet) a User Friendly Error Page as opposed to displaying the typical HTTP ERROR message. The JavaScript could also just as easily modify the SRC attribute to make an entirely different request.
function checkForContents(){
var contents=document.getElementById('myiframe').contentWindow.document
if(contents){
alert('found contents of myiframe:' + contents);
if(contents.documentElement){
if(contents.documentElement.innerHTML){
alert("Found contents: " +contents.documentElement.innerHTML);
if(contents.documentElement.innerHTML.indexOf("FIND_ME") > -1){
openMediumWindow("woot.html", "mypopup");
}
}
}
}
}

I think that the pageshow event is fired for error pages. Or if you're doing this from chrome, then your check your progress listener's request to see if it's an HTTP channel in which case you can retrieve the status code.
As for page dependencies, I think you can only do this from chrome by adding a capturing onerror event listener, and even then it will only find errors in elements, not CSS backgrounds or other images.

Doesn't answer your question exactly, but my search for an answer brought me here, so I'm posting just in case anyone else had a similar query to me.
It doesn't quite use a load event, but it can detect whether a website is accessible and callable (if it is, then the iFrame, in theory, should load).
At first, I thought to do an AJAX call like everyone else, except that it didn't work for me initially, as I had used jQuery. It works perfectly if you do a XMLHttpRequest:
var url = http://url_to_test.com/
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status != 200) {
console.log("iframe failed to load");
}
};
xhttp.open("GET", url, true);
xhttp.send();
Edit:
So this method works ok, except that it has a lot of false negatives (picks up a lot of stuff that would display in an iframe) due to cross-origin malarky. The way that I got around this was to do a CURL/Web request on a server, and then check the response headers for a) if the website exists, and b) if the headers had set x-frame-options.
This isn't a problem if you run your own webserver, as you can make your own api call for it.
My implementation in node.js:
app.get('/iframetest',function(req,res){ //Call using /iframetest?url=url - needs to be stripped of http:// or https://
var url = req.query.url;
var request = require('https').request({host: url}, function(response){ //This does an https request - require('http') if you want to do a http request
var headers = response.headers;
if (typeof headers["x-frame-options"] != 'undefined') {
res.send(false); //Headers don't allow iframe
} else {
res.send(true); //Headers don't disallow iframe
}
});
request.on('error',function(e){
res.send(false); //website unavailable
});
request.end();
});

Have a id for the top most (body) element in the page that is being loaded in your iframe.
on the Load handler of your iframe, check to see if getElementById() returns a non null value.
If it is, iframe has loaded successfully. else it has failed.
in that case, put frame.src="about:blank". Make sure to remove the loadhandler before doing that.

If the iframe is loaded on the same origin as the parent page, then you can do this:
iframeEl.addEventListener('load', function() {
// NOTE: contentDocument is null if a connection error occurs or if
// X-Frame-Options is not SAMESITE (which could happen with
// 4xx or 5xx error pages if the corresponding error handlers
// do not specify SAMESITE). If error handlers do not specify
// SAMESITE, then networkErrorOccurred will incorrectly be set
// to true.
const networkErrorOccurred = !iframeEl.contentDocument;
const serverErrorOccurred = (
!networkErrorOccurred &&
!iframeEl.contentDocument.querySelector('#well-known-element')
);
if (networkErrorOccurred || serverErrorOccurred) {
let errorMessage;
if (networkErrorOccurred) {
errorMessage = 'Error: Network error';
} else if (serverErrorOccurred) {
errorMessage = 'Error: Server error';
} else {
// Assert that the above code is correct.
throw new Error('networkErrorOccurred and serverErrorOccurred are both false');
}
alert(errorMessage);
}
});