detect iframe load error

Question

I am loading a user-selected page into an iframe using the src property. If the load fails, I would like to report the problem in terms that will make sense to the user. iframe

Answer 1

Late to the party, but I've managed to crack it:

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();
});

Answer 2

As you've hinted, you'll face same-origin-policy type restrictions when you try to query anything inside the iframe if it's on a separate domain.

You could make an AJAX GET request to the iframe's URL before you pass it into the src of the frame. If you don't get an HTTP 200 response back from the AJAX call, then the site won't be able to load inside the frame either.

This will add overhead to the whole process, and is only useful if you're checking whether the iframe's document is a real URL that works. It won't help if you need to know when the iframe document has fully loaded.

If you need to know when the iframe has loaded, and it's on an external domain, then I believe you have no other option but to ask for some code to be added to those external sites to notify the parent page that they've loaded successfully.

Or, if it makes sense to do so, ask the end user to click a link to flag up that the content isn't loading correctly.

Answer 3

You could set your iframe and/or ajax request to always call a page you control (ie: loader.php), sending loader.php the user's requested page via get. From loader.php, use curl or even just file_get_contents to fetch the external page. If the request fails to come back to loader.php, you can check the error there, and return whatever you want your iframe to display.

While my example references the use of php, curl is supported in a variety of scripting languages. It is likely more complicated than other solutions you might have, but would give you access to the response headers as well for troubleshooting why a page load failed.