Return of the HTTP overhead delay – this time without a server side component

Tuesday, July 10th, 2007 at 7:44 pm

Following my post yesterday about delaying the loading of avatar images to cut down on HTTP requests I was wondering if there is a way to do this without having to resort to a server side solution. In short, there is.

Using the script is dead easy, simply include it in your page and make sure to include avatar images in the following format:


<img src="default.gif#http://avatarurl" ... >

The default.gif is your placeholder followed by a hash and the real URL. All the script does is go through all the images, check which one has a hash in its src attribute and remove everything up to the hash. If you don’t want to loop through all the images in the document, you can change two variables in the script: You can provide the ID of an element to constrain the loop to in parentID and you can provide a class that is applied to all the avatar images in avtClass. The script is Creative Commons Attibution licensed, so go nuts using it.

Here is the script’s saga: the internet’s Drew McLellan commented yesterday on the blog about the usefulness of the idea and we talked over lunch and then Messenger how we could make it JS-only. First Drew considered the real URL as a parameter after the placeholder, but that messed with the caching as each default.gif?foo would be considered an unique URL. We then thought about fragment identifiers, as for a browser foo.html and foo.html#bar is the same resource.

We weren’t sure about the validity of a real URL as a fragment identifier, and as we are too lazy to look these up I consulted the walking standards encyclopedia, David Dorward and got the green light for the fragment identifier idea. On my way out the office I put the idea past Lawrence Carvalho who thought it necessary to allow for a parent ID and a class to constrain the amount of replaced images. Five stops later on the Picadilly line the script was done and now I am uploading it. It is great to have the right people working next to you.

[tags]performance,httpoverheaddelay,webdevtrick,javascript,images[/tags]

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