Tag Archives: DOM

jQuery tips – storing data

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Storing data?

I was reading an article where the author says it is not a good practice to store data in the DOM. Indeed this is a bad practice and you should avoid it. After that he gives an example with using the DOM with the ALT attribute:

$('selector').attr('alt', 'data being stored');
// later the data can be retrieved using:
$('selector').attr('alt');

and after that the more clean:

$('selector').data('paramtername', 'data being stored');
// then later getting the data with
$('selector').data('paramtername');

OK, is more clean. But however it is bad practice to use such a “heavy” construction to store local data. It is obvious you can prefer to store it in a local variable. Thus you avoid the extra performance.

CSS sprites. Go beyond the limits with base64!

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Why should I optimize CSS?

In fact how and why should I optimize CSS is the right question. Actually CSS is simply one ore more files loaded from the server to the client, usually a browser, with CSS specific rules that must be applied by the browser to the web page you’re seeing. That’s in general. Of course there are exceptions when CSS can be inline or added directly to the HTML tags, which is bad practice because thus the HTML markup becomes larger and even worse the browser cannot cache it and than load it quickly. In fact that’s why usually the CSS of a web page is put in one single file. Primary because that makes only one request to the server and in second hand because it can be cached by the browser.

Just because the nature of the CSS is that firstly it’s loaded and than executed one of the primary techniques of optimizing it is to make it smaller and therefore load faster. There are several methods of doing so. Enabling GZIP support of the web server and minifying the file are the most common ones. But one of the tricks you cannot optimizing just for second is using the so called CSS sprites.

CSS sprites

What are these? To answer this question I’ll simply try to give you an example. Let’s assume there are three CSS classes each one with its own background image. This makes four requests to the server. One for the CSS file and one per every background image. But what we’d like to achieve is to make less requests as we can. Than one of the things we can do is to make one single image and to change only the background-position CSS property to position it on the right place and to make it appear correctly.

Be careful! When you join all of the images into one single CSS sprite you may add one class with that background-image and every other class with only background-position property. Than every DOM element with that background must have both class names. Only than you can be sure the server will make two requests. One for the CSS file and one for the sprite.

base64 to encode images

In other hand most of the web projects are pretty big, and unfortunately it’s too difficult to make only one single sprite just because it’s too difficult to manage it after the project has become very large. That’s why mostly in the practice there are several sprites for the main components. But the problem is that again there are more HTTP requests.

Is there any way to make only one request?

Yes there is. Simply by converting your CSS sprite into a base64 encoded image. In breve base64 is an encoding where you can practically make any data into a string. Thus the image can be represented by a string containing the same information as the image. Hopefully most of the browser, except of course MSIE, does read the so called data urls, or:

<img src="data:image/png;base64,..... " />

and that’s enough to get started with base64 and the single request. The sprite has become a string!

CSS and base64

The natural question is now how to merge all this? You now have one CSS file with one or more sprites. Than you can convert them into a base64 encoded strings and put them all into the CSS.

There is a problem, of course, what happens with MSIE. As I said before MSIE doesn’t read base64 encoded images. Hopefully there is a solution described very well by Stoyan Stefanov in his blog post here.

Finally …

now there is only one request and everything works pretty fine. This technique can be really helpful to someone who’s trying to optimize the CSS performance to the limits.

Optimizing CSS. Five simple steps!

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In the spirit of the optimization wave this post is about CSS optimization. There are some simple rules that you can apply. I’m pretty sure most of us have already been familiar with that list, but you never know.

1. Minify

As the JavaScript the CSS also can be minified. This only strips every character that makes the traffic bigger. As you know a well constructed and pretty looking CSS file consists of many new lines, tabs and spaces. Almost every software minifies the CSS by simply removing them. Some of the programs go even further with replacements of different parts of the code considered to be not efficient.

2. Use effective selectors

Some CSS selectors aren’t really efficient. Imagine something like: body div a just to describe only one specific link. That’s really bad. Better practice is to replace that line with something like a.my-class and to replace the a tag into the DOM with that class name. That will be far more effective. Actually if you’re wondering how to find such bad selectors, there’s a tool by Google called Page Speed that’s a Firebug’s plugin and can extract a list of all bad selectors.

3. Inheritance

CSS is really powerful when dealing with inheritance. That’s something that is not some clear but however really powerful. This technique is in the basics of the next rule.

4. Sprites

I’ve written already about CSS sprites. This is nothing new, but be careful when making a new site’s layout. CSS sprites spend you HTTP request and that’s rule number one according to Steve Souders’ list of optimization.

5. Separate logic

Sometimes developers put the site logic in only one file that become to large. Be aware of that. This is hard to maintain and you load things that you don’t need.

That’s a really short list of what you can do with CSS to speed the site up. I hope that can help someone when dealing with cascading style sheets.

CSS default position value

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position:absolute?

Recently I was working on a problem where some DOM elements inherited the absolute position from their ancestors. Well this is pretty rare, but however it happens from time to time. If you’re wandering, as I was, how to disable this and to call the default property value just stop hesitating. The default property is static. So you can simply write:

#element_id {
   position:static;
}

jQuery live() vs bind() performance

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1. What is event delegation in JavaScript?

To start with some example let’s assume that there is one DIV element with 100 A tags inside. If you assign event to every A tag that as you may know slowes down your browser. That’s a problem because sometimes that can happen, even with more than one hundred A tags. Imagine you’ve a map with one thousand markers, which are A tags. Attaching events slowes down the browser, because every of these A tags bubbles the event that has been fired. And that makes your CPU to make thousands of calculations. Of course you can avoid this problem with a simple technique. Just attach one single event on the container DIV element. Thus you can check if some child of the DIV element has been the target of the event. This makes the browser to breath. Continue reading jQuery live() vs bind() performance →