What if i combine all the CSS of the complete site into a single file.
would it be cached by the browser or be reloaded every single time a new page is opened.
the single css file contains different values for different pages.
should i divide the css for different pages or keep it in a single file?
Yes the files are probably better of combined but will only be cached if the correct headers are set. I suggest downloading YSlow (or Page Speed) which is a plugin for firebug which analyses your page and shows how it is slow and gives advice on how to improve it.
http://developer.yahoo.com/yslow/
Also look at css minification tools like those in the YUI toolkit to compress the css code as well as combining the files.
http://developer.yahoo.com/yui/compressor/
Combining CSS files into one will give you better performance. You can compare this in FireBug( https://addons.mozilla.org/en-US/firefox/addon/1843 ) in FireFox.
If you use asp.net have a look at the ScriptReferenceProfiler, it shows the list of downloaded resources, these can be combined to improve performance: see blog: http://blogs.msdn.com/mikeormond/archive/2008/06/26/asp-net-ajax-scriptreferenceprofiler.aspx
Generally speaking, combining your CSS into a single file is a good practice for production servers. The single file reduces the number of http requests required and, in both cases (single or mutiple files) caching will be used.
The benefit of fewer http requests is greatest for first time visitors.
Also, you reduce the number of requests required on subsequent pages as the file will have been cached. (think of it as pre-loading the css if the portions unused on the current page seems wasteful to you)
Most sane browsers will cache CSS files, so compacting them down into a single file can help a little when it comes to request times. However, maintainability is also an issue - if you have difficulty maintaining the CSS code when it's all in a single file, you may still want to stick with separate files.
In the end it's up to you, whatever feels best.
It is is good to have one file. Please see for the file size also that might affect the page load time. All browser catch the css files. Next time it will not load new one.
Please use the yahoo info for that.
Related
I like the idea of encapsulating my CSS into separate files. This also brings the added advantage of being able to easily minify the CSS. But I know performance is negatively impacted by the overhead needed to pull these separate files from the server.
To address the latter point, people often suggest inlining the style or at least putting the CSS in the HEAD of the html document. I'm not going to inline because then editing the style becomes a nightmare. I can consider putting it in the head to increase performance, but I do not want to put it in there minified. I won't be able to read it, and it will be a pain to have to adjust the CSS once minified.
So my question is, What is the better option -- in terms of performance -- between these two?
Minified external CSS file
CSS placed in the HEAD but not minified
You are not considering browser-side caching in your evaluation. It is almost ALWAYS better to serve up CSS in an external file for cases where you will be using the same CSS file throughout a multi-page website. The reason for this is that once the CSS is downloaded on first page visit, assuming you have expiry headers set properly, the browser will not need to download the CSS on subsequent page loads until the expiry TTL is passed. This even holds true across multiple user sessions on a website, such that if a user visits the sites some days/weeks later, they may not need to download the CSS at all. If you served up in-page CSS, it would need to be downloaded on every page load.
Also minifying is typically not that big of a performance boost, as most server to browser connections will perform text compression on transmitted content anyway.
Of course it is also usually much easier to maintain CSS in an external file as you have pointed out.
The best option would be to:
Minify them all and bundle them in the server side with something like bundles for Asp.Net or brewer for nodejs, that way you remove the overhead you mentioned above.
To expand on my comment:
Generally, when optimising web page loading, you want to minimise the number of HTTP requests that the browser makes as these are expensive, time-wise; even requests for small files require the browser to send its request to a server, wait for the response, and then act accordingly. From that perspective, the best thing would be to put all the code for your page into a single file. However, this would be a page maintenance nightmare, and it also fails to take into account caching of resources by browsers, as covered by #MikeBrant.
A single css file (potentially composed of several concatenated minified files) is a good compromise between separation of style (css) and content (html), and performance. The same applies to javascript. You can also consider using a content delivery network (CDN) for Javascript if you're using a common library like JQuery as the user's browser may already have the library cached from visiting another site. Google's CDN serves a number of useful libraries.
Generally, you'll get far bigger performance gains from optimising images, enabling server compression, and removing extraneous javascript than you will from minification or inlining CSS. Images are almost always the "heaviest" elements of a page, and it is often very easy to reduce image size by 20-50% and maintain decent quality.
I'm testing a website speed using PageSpeed Insights tool.
In the result page, one of the warnings suggested me to reduce byte size of css, html and js files.
At the first I tried to remove comments, but nothing changed.
How can I do that?
Should I remove spaces and tabs?
It seems to be a very long operation, worth it?
The action of removing spaces, tabs and useless chars is called minify.
You don't need to do that, there are a lot of services that can minimize files for you.
for example:
http://www.willpeavy.com/minifier/
Be care if you have jquery code: sometimes it removes spaces in wrong place.
You have two things to do to reduce page size:
Minify CSS & JS files
In server side, if you are running your website via Apache, you can install APC, for page cahing. You'll have better parformances
APC
In addition to CSS minifier/prettifier tools above, I recommend using proCSSor for optimizing CSS files. It offers variety of advanced options.
Never found those tools to be much use beyond giving some tips for what might be slowing it down. Minifying is unlikely to achieve much. If you want to speed up your site, save the page and see what the largest files are. Generally they will be the image files rather than the code, and see if you can reduce these.
Also, try and test it on two servers - is your host slow?
If your html file is massive, that suggests a problem with the site's structure - it is rare that a page needs to be large.
Finally, large javascript files are most likely to be things like jquery. If Google hosts these, then use the hosted version. That way, it will probably be already in a user's cache and not impact on your loading time.
EDIT, after further testing and incorporating the issues discussed in the comments below:
PageSpeed Insights is an utterly amateurish tool, and there are much more effective ways to speed up the rendering time than minifying the codes.
PageSpeed Insights is an utterly amateurish tool, that as a matter of standard advises to reduce HTML, CSS and JS file sizes, if not minified. A much, much better tool is Pingdom Website Speed Test. That compares rendering speed to the average of the sites it is asked to test, and gives the download times of the site's components.
Just test www.gezondezorg.org on both, and see the enormous difference in test results. At which the Google tool is dead wrong. It advises to reduce the CSS and JS files, while its own figures (click the respective headers) show that doing so will reduce their sizes with 3.8 and 7.9 kB, respectively. That comes down to less than 1 millisecond download time difference! (1 millisecond = 1/1000 of a second; presumed broadband internet).
Also, it says that I did do a good thing: enable caching. That is BS as well, because my .htaccess file tells browsers to check for newly updated files at every visit, and refresh cached files whenever updated. Tests confirm that all browsers heed that command.
Furthermore, that site is not intended to be viewed on mobile phones. There is just way too much text on it for that. Nevertheless, PageSpeed Insights opens default with the results of testing against mobile-phone criteria.
More effective ways to speed up the rendering
So, minifying hardly does anything to speed up the rendering time. What does do that is the following:
Put your CSS codes and Javascripts as much as possible in one file each. That saves browser-to-server (BTS) requests. (Do keep in mind that quite a number of Javascripts need the DOM to be fully loaded first, so in practice it comes down to putting the scripts as much as possible in 2 files: a pre- and a post-body file.)
Optimize large images for the web. Photoshop and the likes even have a special function for that, reducing the file size while keeping the quality good enough for use on the web.
In case of images that serve as full-size background for containers: use image sprites. That saves BTS requests as well.
Code the HTML and JS files so that there is no rendering dependency on files from external domains, such as from Twitter, Facebook, Google Analytics, advertisement agencies, etc.
Make sure to get a web-host that will respond swiftly, has a sufficient processing capacity, and has a(n almost) 100% up-time.
Use vanilla/native JS as much as possible. Use jQuery or other libraries only for tasks that would otherwise be too difficult or too time-consuming. jQuery not only is an extra file to download, it is also processed slower than native JS.
Lastly, you should realize that:
having the server minify the codes on the fly generally results in a much slower response from the server;
minifying a code makes it unreadable;
de-minifying tools are notorious for their poor performance.
Minifying resources refers to eliminating unnecessary bytes, such as extra spaces, line breaks, and indentation. Compacting HTML, CSS, and JavaScript can speed up downloading, parsing, and execution time. In addition, for CSS and JavaScript, it is possible to further reduce the file size by renaming variable names as long as the HTML is updated appropriately to ensure the selectors continue working.
You can find plenty of online tools for this purpose, a few of them are below.
HTML Minify
CSS Minify
JS Minify
good luck!
That's it. I've been hearing about CSS files a lot.
What are the main advantages of having a CSS file instead of writing the styles in the HTML code directly?
Assuming your site has 10 pages
You don't have to repeat yourself 10 times.
If your style changes, you don't have to do the change in 10 files
Your HTML files are smaller
Your CSS files can be cached
You can reuse the style sheet on other sites you make
I'd add to JohnP's excellent answer by saying:
you can separate out your caching
on your page (where content may
change regularly) to your CSS (where
it may not) - sites are more likely
to cache CSS for longer than they
would the content of a page,
separating it out will allow you to
do this
you can deliver your CSS
from a content delivery network,
potentially improving site
performance
you can 'minify' your
CSS as part of a build process so
that what you're developing on is
readable/verbose, and what you
deliver is small/terse, again as a
means of improving performance
once the content and presentation
are separated out, your users will
benefit from all of the above and
you will get a faster page load.
Please read this artical on Advantage of using external css.
There are a few advantages;
1) You can re-use the CSS in different pages across your site.
2) The download is separate for CSS when it is in a separate file, this is quicker.
3) The separate CSS file will be treated as static content and likely cached locally. Again quicker.
I personally find CSS easier to read and edit when it is in its own file.
Some good answers by JohnP. However, the most important reason for me would be the separation of presentation and content.
Versioning becomes far easier as you have a central point to apply changes.
The loading time of your site advances because you only deliver the stylecode ONCE and not with every html page you deliver.
Furthermore you save up loading time as the css can be cached locally and so the site loads faster after first load, if there was no changes. This can also cause problems, see solution for those problems in point 2.
you can also use different styles for different platforms or different tasks (such as braille or print)
see available types here:
Media types
There are severe cache problems regarding Internet Explorer, you can give version numbers to keep the cached css out of order, if there were changes applied, so there is NO disadvantage of using css files but a HUGE advantage in administering the site.
Example of versioning:
<link rel="stylesheet" href="[path_to_css]/style.css?v=[date]" type="text/css">
So there are only huge advantages and no disadvantages of using css, so it is best practice.
Sometimes on completely valid browsers, but a hindered Internet connection, the webpage loads without some of the external css files, resulting in a ugly webpage.
Is there a way to prevent this without resorting to embedding all of the css in the html?
I guess you might be hitting the timeout when hitting the CSS file. You might try caching the CSS file on the client side by using far future headers. And minify the CSS so it has a small file size and can be quickly grabbed.
Try to use less css files as much as possible because ever single css files send different http request so, when there are less css files that means less http request .Which automatically increase the speed & minify the css also .
A general rule of performance is to reduce the number of HTTP transactions. This is particularly important in these days of add-ins. Each HTTP transaction adds an overhead of about 1kB up and down by adding the headers. It adds load on the server and delays rendering. It also opens up the risk of network timeouts -- especially a problem on 3G phone networks.
Regarding CSS, it's better to have a single larger file than lots of smaller ones to avoid exactly the problems you're experiencing. If you minify the file -- but don't optimise it -- it will also get rid of the comments and white space.
Similarly it's worth combining jQuery addins into a single file for the same reasons.
Would it be wise to combine all CSS into a single file? Would there be any performance increase. I have to assume that an HTTP request is made to get each file on initial page load, and reducing those requests would seem to make sense.
Are there any reasons NOT to combine all css into a single file?(such as maintainability or other performance issue)
Merging all of your css files into one will absolutely gain performance. Whether that performance is noticeable depends on your load, number of requests etc. For the average blog, this will have close to zero impact.
Read Best practices for speeding up your web site at Yahoo! Developer. It'll explain things way better than i can.
As you say, a reason not to merge css files is for maintainability. However, there are many tools out there which automatically merge and minify your css files into one.
You should check out YUI Compressor, this will help you with merging and minifing your css files.
Would it be wise to combine all CSS
into a single file? Would there be any
performance increase. I have to assume
that an HTTP request is made to get
each file on initial page load, and
reducing those requests would seem to
make sense.
Yes, but make the combination at build or runtime and don't try to maintain a single file if you started with multiple ones.
In addition to the number of HTTP requests it is also important to set the right expiration headers in the response.
Are there any reasons NOT to combine
all css into a single file?(such as
maintainability or other performance
issue)
It is not necessary to maintain a single file, but good to serve a single file, because CSS data is anyway merged.
The YUI Compressor is a good tool for JavaScript and CSS minification.
Would it be wise to combine all CSS into a single file? Would there be any performance increase. I have to assume that an HTTP request is made to get each file on initial page load, and reducing those requests would seem to make sense.
Yes, yes, yes.
Are there any reasons NOT to combine all css into a single file?
No
(such as maintainability
Combine them at build time and not at development time an there won't be a maintainability problem.
When not all page need all the css then splitting it in multiple files might be faster.
Maintainability becomes an issue if the CSS file gets really huge, when different teams need to coordinate their work on it.
There might be another reason, to NOT combine files:
If the combined stylesheet file is getting too large, Internet Explorer 9 will ignore some of the styles..
See: IE 9 ignoring CSS rules