Tag Archives: Minification

More on CSS Optimization

As CSS files are first downloaded to the client and then executed, the main optimization is to make those files smaller. But that doesn’t mean only minifing!


The Minification Process

While with minification you can strip all the symbols that only take space, but are useless when the browser parses the file, there are some other techniques, which in fact aren’t so simple, to speed up the loading process. By minification you get rid of the white spaces, tabs, new lines, etc., but the file may remain too large.

Useless Rules

Yes, sadly the browser doesn’t need all those white spaces, actually web developers need them. Just because this makes the file more readable, or readable at all. However most of the web applications have one large CSS file, typically named layout.css, main.css or whatever, that contains all the rules for the entire application. In many of the cases one page of a site doesn’t need all the rules for the site, so a possible solution is to remove all of the rules that aren’t used.

There are tools that may help you do the job. Such a tool, that I’m using is the Firefox add-on – Dust-Me Selectors. Of course there are a lot other tools doing the same job, so it’s up to you to pick up one.

After removing all those useless rules you’ll see that the size of the file can be something like 20% of the size of the source file. This is interesting to note, because most of the time the minification cannot give you such performance benefit. In fact this comes with some issues.

One Request or What?

This is the dilemma of the web programming, isn’t it? However thus you can split the main CSS file to few smaller files, but they are named differently so you cannot expect the browser to cache them when the user visits the site for the first time.

The case must be, of course, tested against various situations, so you can decide what suits you. However the typical scenario is to optimize only few of the pages, as they might be the most visited – as for example the homepage. If two of the pages are mainly visited, than you can make custom, small, CSS files for them with only the necessary rules, and let the other pages with the main CSS file. If you’ve a lot of returning visitors, you can be sure the custom files will be cached (if the client cache is turned on) and the second time somebody visits the “homepage” for example the page will load faster.

CSS sprites. Go beyond the limits with base64!

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.

Speed up the JavaScript. It can change dramatically the user experience.

JavaScript in a modern web application

If someone asks you what is the javascript in modern web developer, probably you should answer it’s almost the half of the traffic of your site and it’s almost everything when dealing with user experience.

Today’s big web apps are useless without it AJAX/JS part. Think about Facebook, Google products, Twitter, Yahoo!, Youtube.

Actually they made this a standart. The times when you used to use JavaScript as a helper language just to figure out how a drop down menu will work are far way in the past. Now JavaScript is everything in a rich web sites. With no JS they will be no rich at all! Then it comes the question how to improve sites with lots of javascript. Actually one of the main problems in the web now is that JavaScript is blocking content.

Blocked by the JavaScript

What that means at all is that until the browser receives and parses the JavaScript file/s it doesn’t process anything else, it even doesn’t load any other resources. Now you can imagine how big the problem is. When it comes to large files more than 100K the user experience will be very bad!

Optimize the web? What about optimizing JavaScript!

If the problem is so big as I described above why should we doubt about where to start with the optimization process? But of course with the JavaScript and the natural question that rises is how this can be optimized at all?

Three steps

Like me, many of you may heart of some techniques that improve javascript performance. Here are some I was able to select as important:

1. minify/compress

That’s rule number one. If everything that is a JavaScript file is processed once it arrives to the client than make it smaller and make it go faster trough the wire. Actually one technique to speed up things more is to concatenated all the files you have into one single big file. Although this will not spend you some space will reduce the HTTP requests and therefore speed up the loading process. Good tools that you can use to minify javascript files are the Yahoo’s YUI Compressor, that beside that compresses CSS and Google Closure Compiler. Both are extremely useful and by the last measurements the Google’s Compiler is even better, but it’s up to you to decide which one to pick up.

2 .write fast and smart code

You can minify everything that’s JavaScript and the code may remain slow. But why is that? That’s because the JavaScript is written in a bad way. You know there are many resources in the web describing what is a bad and what is a good practice when writing JS. Even more you can measure it by yourself if you’d like to use the Firebug’s profiler. That’s a good start to avoid bad practices.

3. improve loading – lazy loading

That’s a bit more complicated. If there’s a really big javascript file after compressing and concatenating all the JS functionality remains big. How to avoid that? Simply let’s the user to see the most important functionality and than load the entire app. Some good tutorials about lazy loading again can be found online. Don’t hesitate to search about.

Beside this really basic advices I’ll continue to write in my blog about specific techniques how to improve the JavaScript as this is one of the most interesting parts of web development by me.

Optimizing CSS. Five simple steps!

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.

What should I optimize first in my web page?

I start with the optimization process …

It’s a common question! Where do I begin with the optimization process. Should I start with JavaScript or with some simple Apache optimizations? The answer is pretty simple and it’s related to a very, very simple technique.

Look what Firebug is saying

Yeah, look at the Firebug. You can check what’s taking most of the time to load. If it’s some server site script you can try caching it, if it’s a JavaScript file load, than you can try minify/compile it. Another good tool is the Safari developer tool. Than you can graphically understand what part of the sites’ components are slowing down the loading process. Whether the images or the JavaScript, well check that out with the Safari browser.

Finally what I do?

Once you know what’s the thing slowing down the site, start with its optimization! It’s really simple.