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.

Answer 2

I would extend Sijin's answer by saying:

An HTTP HEAD request to the url can be used to examine the resource's mime-type. You won't need to download the rest of the file that way.

Answer 3

Completely untested, basicly just an idea:

function isImage(url)
{
    var http = getHTTPObject();
    http.onreadystatechange = function ()
    {
        if (http.readyState == 4)
        {
            var contentType = http.getResponseHeader("Content Type");
            if (contentType == "image/gif" || contentType == "image/jpeg")
                return true;
            else
                return false;
        }
    }

    http.open("HEAD",url,true);
    http.send(null);
}


function getHTTPObject() 
{
    if (window.XMLHttpRequest)
    {
        return new XMLHttpRequest();
    }
    else 
    {
        if (window.ActiveXObject)
        {
            return new ActiveXObject("Microsoft.XMLHTTP"); 
        }
    }
    return false;
}

Answer 4

I am not sure the of the exact setup you have, but can you use the HTTP response and check the mime-type to determine image vs flash?

Answer 5

If the URL doesn't have an extension then there is no way to tell without requesting the file from the server.