Question

I would like to poll an anchor’s href source about once every 5 seconds, to see whether a file at that address is present. When it is present, display an image in the anchor. In other words, the link is basically not there unless the file is present.

I’m guessing I would have to poll using an http HEAD request to determine whether the file exists, then toggle the image appropriately. Once the file has been determined to exist, I can stop polling and leave the image visible.

Is there a better way to do this, and can anyone suggest some script that would handle this functionality?

Answer 1

If your server is configured to do so you can use:

http://api.jquery.com/jQuery.ajax/

To poll for the file’s existence by using the statusCode map

function checkFile() {
    $.ajax({
        statusCode: {
            404: function() {
                //file does not yet exist
                setTimeout(checkFile, 5000);
            }
            200: function() {
                //file exists.
                showImage();
            }
        }
    });
}

You may want to capture a few more edge cases though, (for example, an error callback).