Comments on: Getting a fully qualified URL

By: James

James — Mon, 19 Oct 2009 20:36:23 +0000

@Kyle, thanks for the “http://” tip!

@Zach, funnily enough, that StackOverflow thread you just linked to was started by me (“J-P”)!

By: Zach Leatherman

Zach Leatherman — Mon, 19 Oct 2009 20:22:50 +0000

Actually, a co-worker pointed out to me that the removeAttribute will not work properly either. I found a silver-bullet approach using innerHTML over at http://stackoverflow.com/questions/470832/getting-an-absolute-url-from-a-relative-one-ie6-issue

By: Zach Leatherman

Zach Leatherman — Fri, 16 Oct 2009 19:18:21 +0000

Instead of
img.src = null;

This should work without making a request:
img.removeAttribute(‘src’);

I would strongly encourage you to amend the article with this information, I was seeing serious issues with corrupted server-side models because of this extra “null” request, which would resolve to something like:
http://james.padolsey.com/javascript/null

Thanks,
Zach

By: Kyle Simpson

Kyle Simpson — Thu, 07 May 2009 15:15:37 +0000

I just tried this in IE7.

Results: a request is made when you set img.src, but then it looks like it’s canceled when you set src=null. So, technically, a request is fired off, but the page isn’t suffering from the waiting for the response.

However, I watched the server logs, and the server doesn’t even receive the initial request, but it does receive the request for “null”, which of course (usually) will return a 404. So that kind of defeats the purpose. Trading one request for another isn’t that helpful.

However, if you set img.src = “http://”, then it makes a dead request (no server load taken up), and should have little to no overhead in the browser processing/waiting (since this is javascript and asynch/non-blocking).

The bad part is the server does still receive the initial script url request (in the logs), but again, IE7 has already abandoned the request by that point so the browser doesn’t pay the penalty to process the response.

————-

Also, I tried the a.href stuff, and that doesn’t work when inserted by javascript, at least not in IE7. It just returns the same src you set to it. I even tried inserting the link into the body of the page, still no go.

By: James

James — Thu, 22 Jan 2009 21:33:05 +0000

Technically, a server request is made but since the ‘src’ is set to null it just ends up being a request to the same page which means the overhead is non existent (I’m not totally sure about this though). It might be worth introducing a compromise:

function qualifyURL(url) {
    var a = document.createElement('a');
    a.href = url;
    if (/^http:\/\//.test(url)) {
        // IE7, FF, Op, Sf
        return a.href;
    } else {
        // IE6
        var img = document.createElement('img');
        img.src = url;
        return img.src;
    }
}

By: Thomas Milburn

Thomas Milburn — Thu, 22 Jan 2009 19:15:36 +0000

It might not be completely your own but I like your modification and its a neat hack! Could you explain how your modification actually works. When would javascript normally make the server request. I would of thought it makes the server request when the image’s src is first set.

By: James

James — Thu, 22 Jan 2009 08:21:14 +0000

Thanks all!

Yep, Thomas, you’re correct, although I made my own little modification which prevents any server requests from being made. I suppose I shouldn’t have called it “my magical method”; I guess I’m just a fan of alliteration!

By: Thomas Milburn

Thomas Milburn — Thu, 22 Jan 2009 08:05:43 +0000

I presume James got the idea from here.

By: Brenelz

Brenelz — Wed, 21 Jan 2009 23:25:12 +0000

Wow… neat trick James!

How did you find this one out?

By: Joseph McCann

Joseph McCann — Wed, 21 Jan 2009 23:06:50 +0000

Very interesting…well done James.