how to detect if a URL points to a SWF

Question

Is there a way (preferrably using JavaScript) to determine whether a URL is to a SWF or a JPG?

The obvious answer is to sniff the filename for ".jpg" or ".swf" but I'm dealing with banners that are dynamically decided by the server and usually have a lot of parameters and generally don't include an extension.

so i'm wondering if I could load the file first and then read it somehow to determine whether it's SWF or JPG, and then place it, because the JavaScript code I'd need to display a JPG vs a SWF is very different.

Thanks!

Answer 1

You could use javascript to detect if it is a image by creating a dynamic img-tag.

function isImage(url, callback) {
    var img = document.createElement('img');
    img.onload = function() {
        callback(url);
    }
    img.src = url;
}

And then calling it with:

isImage('http://animals.nationalgeographic.com/staticfiles/NGS/Shared/StaticFiles/animals/images/primary/bald-eagle-head.jpg', function(url) { alert(url + ' is a image'); });

Update This version will always execute the callback with a boolean value.

        function isImage(url) {
        var img = document.createElement('img');
        img.onload = function() {
            isImageCallback(url, true);
        }
        img.onerror = function() {
            isImageCallback(url, false);
        }
        img.src = url;
    }

    function isImageCallback(url, result) {
        if (result)
            alert(url + ' is an image');
        else
            alert(url + ' is not an image');
    }

Put your logic in the isImageCallback function.