Loading images last with jQuery

Add to FacebookAdd to DiggAdd to Del.icio.usAdd to StumbleuponAdd to RedditAdd to BlinklistAdd to TwitterAdd to TechnoratiAdd to Yahoo BuzzAdd to Newsvine

There are lots of ways to make your webpages faster and more responsive. YSlow is a great tool to help you find many great ways to make a particular page faster.

One of the best things you can do is reduce the number of requests (css/js/images/etc) to the server. Typically, this would mean that you would combine files – merge all of your JS and CSS (and minify while you are at it), and use CSS Sprites to combine images.

One major problem of using CSS Sprites is that it can be quite painful to maintain. Over time, if you want to add or change some of your images – you basically need to rebuild and replace the combined images and all of the CSS rules specifying coordinates. Sometimes, this makes the CSS Sprite technique unreasonable to implement.

In one such case, we had about 50 images in one application that were causing the page to take a long time to load. These images were previews of some different design choices that the user could make. The design choices themselves (and their previews) were database driven so that we can add new designs through an admin interface. So, CSS Spriteing the previews would seriously hamper that flexibility.

One other design consideration was that the previews weren’t that important – the page was fully functional and usable without the images. In fact, the designs weren’t even visible until you toggled the design menu.

There is a lazy loader plugin for jQuery already available here – but it didn’t fit our needs. Instead of skipping images in order to get the page working as soon as possible (and initiate the load once the page is usable) – it is made to skip loading offscreen images until they are scrolled into view. It might have somewhat worked for our needs – but I thought it was better to load the images as soon as possible, instead of waiting for the design menu to be expanded to initiate the load. That way, most of the time the designs would be visible by the time they open the menu – but it wouldn’t interfere with the rest of the interface.

My solution was to set the src for all of the previews to a single animated loading image – like one you can get here. Then, I set a custom attribute on the image for the real preview’s url. Finally, some jQuery code runs after the page is done loading which replaces each src attribute with the url in the custom attribute, which will load the real image.

Sample HTML:

<ul>
    <li templateid="7bcf8f23-fdd0-45c5-a429-d2ffb59e47f0" class="selected"><span>3D Dots
        Dark</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/7bcf8f23-fdd0-45c5-a429-d2ffb59e47f0/preview.jpg"
            class="deferredLoad" alt="3D Dots Dark" />
    </li>
    <li templateid="b1a09e28-629e-472a-966e-fc98fc269607"><span>3D Dots Lite</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/b1a09e28-629e-472a-966e-fc98fc269607/preview.jpg"
            class="deferredLoad" alt="3D Dots Lite" />
    </li>
    <li templateid="e121d26a-9c8f-466f-acc7-9a79d5e8cfa9"><span>Beauty</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/e121d26a-9c8f-466f-acc7-9a79d5e8cfa9/preview.jpg"
            class="deferredLoad" alt="Beauty" />
    </li>
    <li templateid="322e4c7a-33e7-4e05-bb72-c4076a83a3d0"><span>Black and White</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/322e4c7a-33e7-4e05-bb72-c4076a83a3d0/preview.jpg"
            class="deferredLoad" alt="Black and White" />
    </li>
    <li templateid="57716da9-91ef-4cf0-82f1-722d0770ad7f"><span>Blank</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/57716da9-91ef-4cf0-82f1-722d0770ad7f/preview.jpg"
            class="deferredLoad" alt="Blank" />
    </li>
    <li templateid="a79e1136-db47-4acd-be3e-2daf4522796d"><span>Blue Leaves</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/a79e1136-db47-4acd-be3e-2daf4522796d/preview.jpg"
            class="deferredLoad" alt="Blue Leaves" />
    </li>
    <li templateid="03cb737d-4da7-46d5-b4e4-5ad4b4a3aaf4"><span>Blue Open</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/03cb737d-4da7-46d5-b4e4-5ad4b4a3aaf4/preview.jpg"
            class="deferredLoad" alt="Blue Open" />
    </li>
    <li templateid="899dff2f-38ba-44f7-9fe2-af66e62674a4"><span>Compass</span>
        <img src="/static/img/ajax-loader-small.gif" deferredsrc="/resources/899dff2f-38ba-44f7-9fe2-af66e62674a4/preview.jpg"
            class="deferredLoad" alt="Compass" />
    </li>
</ul>

Sample javascript:

$(function(){
        $("img.deferredLoad").each(function() {
            var $this = $(this);
            $this.attr("src", $this.attr("deferredSrc")).removeClass("deferredLoad");
        });
});
Advertisements

2 Responses to “Loading images last with jQuery”

  1. Designerfoo™ Says:

    But, won’t this cause HTML Validation problems? using “deferredsrc”, you can use “rel” instead?

    • Brian Grinstead Says:

      You are right that this would cause HTML Validation problems. An alternative would be to use the HTML5 Dataset attributes. It would then at least validate under HTML5 rules.

      data-deferredsrc=”/resources/…”

      I don’t think that “rel” is a valid attribute on an “img” tag. I believe it is only valid for certain tags, like “a” and “link”.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: