The Fastest Website is an empty webpage, after that each bit of data added compromises performance, But this load is on the server to send all code to client,
Now, If I use bootstrap or any css library in general, from a CDN, all the processing happens in client after fetching the stylesheet, this causes a lot of delay,
So, If I include complete bootstrap stylesheet (pretty huge), and put it in a <style> tag on my Single Page App, all the load would be on the server, but that would be negligible compared to load on client as it is just plain text,
So, Is it just efficient enough to include all CSS code in my page itself?
CDN is always faster than your css file which will come from your server and moreover CDN also keep cache on client side from different website as well which will give your website an advantage of getting load faster.
My recommendation would be to use CDN rather than your own css for bootstrap
So I know generally it is not best practice to have multiple css files placed within the head tag of your site due to the increased number of http requests you would have to make. Therefore it has been recommended to me to just use one big css file instead of smaller ones. However, wouldn't it make sense to break up that css file into separate, smaller files, and then link those individual css files only on the pages where they are needed? So say my homepage had its own set of styles, and my about page obviously will differ from my homepage with it's own set of styles. So why not link a homepage.css file to the html homepage and then only link an about.css file to the html about page? There is still only one http request being made in each case, and you can have much smaller css files. Is there something I'm missing?
CSS is cached, so that if you were to link to your big CSS file on your homepage (lets say domain.com/css/homepage.css) then the user travels from your homepage to the about page and it calls the same homepage.css, but you're browser then says "wait! I already have it!" and it skips the HTTP request for the file, resulting in no additional requests.
Where as you have a CSS file for each page, there would be a request for nearly identical CSS files that is wasting bandwidth needlessly. It may not seem like a big deal on smaller sites, but bigger sites with 1000s of requests happening, the extra bandwidth adds up and results in higher operating costs.
The only exception to this is when you're using a responsive framework of some sort (like bootstrap) where editing the main bootstrap file is either impossible (through CDNs) or impractical and hard-to-maintain (i.e. when bootstrap updates you'll lose all your customization), which in this case you would have one bootstrap.min.css file and one custom.css that allows you to keep your customizations while only increasing bandwidth slightly.
For resources like CSS and JS, these things are normally separate resources (which each require separate a HTTP request/response to get). But they can be inlined to reduce the number of separate resources.
I am wondering if the same sorta thing could apply to images.
Maybe include the images in the header?
Or inline in the actual HTML (in Base64 encoding or something)?
(1) Is this possible? (2) Is this a good idea? (why or why not?)
For reducing requests related to images, you can use CSS Sprites / Image Sprites which combines all the images in a single image (so only 1 request to server), which can then be shown as different elements using CSS
Refer W3Schools guide for more information
Spritepad is a good tool to generate image sprites
Inline HTML for images using base64 can become bulky as it would be downloaded everytime the page is fetched instead of caching the image
What do you think is the best for website performance ? Load a different css per page (minified of course), so there won't be any unused css rule in this file, or load the same big (minified too) css in every page of the site ?
The question could seem obvious, but I am wondering about the browser cache... if the big css is loaded in the browser cache, it won't be reloaded in each page, no ? So, maybe it is better to have a lot of unused css rules, but one file which is not reloaded every time than multiple files that we have to load when you browse the website.
Thanks !
It is better to have one big minified css with all the rules, that way you are reducing the amount of connections the browser attempts to do to the server, as well as only one CSS gets cached for every request.
Actually this is what most minify tools do, they compress all of the files in only one CSS file for the whole application.
The other approach for performance is to use Content Delivery Networks (CDN) to load common CSS or JS from the internet.
I want that my html page loads faster as it can. So I'm trying to put all CSS styles into the same .css file and all JavaScript code to the one .js file. How my colleagues told me it makes web page load faster. I want to ask some questions about it.
Just to be sure: Are my colleagues right? On which situations it's better to break CSS or JS code to the separate files?
Question is: If I have a lot of small icons on my page, like "delete, edit, add", should I load image with all icons at once or each icon separately? If I'll load all icons at once, how do I select desired one, if icon's size is 40x40px?
Thank you!
Are my colleagues right?
Single files can be downloaded with single HTTP requests (with single sets of HTTP headers, etc, etc) and can be compressed more efficiently then multiple files. So from a performance perspective, if you need all the content, it is better to place them in a single file.
On which situations it's better to break CSS or JS code to the separate files?
When you need a specific page to load very quickly (e.g. the homepage) or when there are sections of the site which use a large chunk of script that isn't used elsewhere then it can be beneficial to break the files up then.
If I have a lot of small icons on my page, like "delete, edit, add", should I load image with all icons at once or each icon separately?
From a performance standpoint, the same rules apply. However, there is no way to specify that a content image (and icons that don't decorate text are content images) is just part of a larger file. You have to use hacks involving background images. This breaks the separation of concerns around content and style and usually involves using semantically incorrect elements, and then requires further hackery to provide alternative content for users who can't see the image and that hackery rarely does as good a job as an alt attribute.
If I'll load all icons at once, how do I select desired one, if icon's size is 40x40px?
You have an element with specific dimensions and a background image with background-position set so that only the part of the image you want shows through.
Consolidating your CSS and JS code into a shared file will improve load times on all loads after the first so long as the browser uses the version of the file in its cache rather than downloading it again. There are many factors that can affect this, but under normal circumstances it should work.
Also, make sure your image files are stored in the same resolution as they will be displayed. Displaying a 40 x 40 pixel file at 20 x 20 pixels means that you have download four times the necessary image size. If the same icon file is referenced many places in an HTML document, then that icon file will only be downloaded once, so it will have little effect on page loading times.
For putting all the icons into one file and choosing which one, see this:
http://cssglobe.com/post/3028/creating-easy-and-useful-css-sprites
You can use what they call CSS sprite.
The thing is very simple to think of but can be a little tricky to use. Here is the idea.
You merge all your images into on big image, making it a single load.
Wherever these images were used on the site, you replace it by a css class which use the big image as a background and a certain positioning.
Let's say you merge 4 image together : delete.png, add.png, edit.png, share.png.
You create a css class for everyone of these like so :
.delete{ background-image:url('../img/icons.png');
background-position:0px 0px;
}
.add {background-image:url('../img/icons.png');
background-position:0px 40px;
}
.share {background-image:url('../img/icons.png');
background-position:40px 0px;
}
.edit { background-image:url('../img/icons.png');
background-position:40px 40px;
}
This way, you reduce the number of request since you you use a single image to show everywhere.
The code was written on the fly, tell if something is wrong.
Also have a look at performance guru tools : Page Speed
Breaking CSS files is not really a problem, considering browser caching.
Breaking up JS files is okay. You can have one JS that handles things needed for the page to load in the <head> tag. And one js that gives interaction to you, after </body>. By doing this you won't have various effects, but you ensure your users sees your text content.
Regarding your images, there's a practice called CSS Sprites. You can use that to make one big file for your small images and use CSS background-position to show only the part you want. It's like cropping your image file based on the css class.
If speed is most important, then what you've been told is correct.
Less CSS and JS files means less HTTP requests to the server. I would only separate files if you have a specific need as part of a project (eg they need to be maintained in ver separate ways)
For JS I always load JQuery and other libraries from the Google CDN - this has a greater performance boost that merging the library into your code as users are likely to have a cached version of Googles code.
For icons I would use CSS sprites (again this means fewer requests to the server) or if you really want to go as far as possible - look into embeding Data URI in your CSS.
Further reading
Googles Page Speed tool
Data URI in CSS
If you want a better performance report about your page, you can take a look at these tools
YSlow: http://developer.yahoo.com/yslow/
PageSpeed: http://code.google.com/intl/es-ES/speed/page-speed/docs/overview.html
Both can be added into the FireBug plugin (Mozilla Firefox).
From YSlow documentation:
Minify JavaScript and CSS
tag: javascript, css
Minification is the practice of removing unnecessary characters from code to reduce its >size thereby improving load times. When code is minified all comments are removed, as >well as unneeded white space characters (space, newline, and tab). In the case of >JavaScript, this improves response time performance because the size of the downloaded >file is reduced. Two popular tools for minifying JavaScript code are JSMin and YUI >Compressor. The YUI compressor can also minify CSS.
Obfuscation is an alternative optimization that can be applied to source code. It's more >complex than minification and thus more likely to generate bugs as a result of the >obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a >21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size >reduction, minifying JavaScript is less risky.
In addition to minifying external scripts and styles, inlined and blocks >can and should also be minified. Even if you gzip your scripts and styles, minifying them >will still reduce the size by 5% or more. As the use and size of JavaScript and CSS >increases, so will the savings gained by minifying your code.
Preload Components
tag: content
Preload may look like the opposite of post-load, but it actually has a different goal. By >preloading components you can take advantage of the time the browser is idle and request >components (like images, styles and scripts) you'll need in the future. This way when the >user visits the next page, you could have most of the components already in the cache and >your page will load much faster for the user.
There are actually several types of preloading:
•Unconditional preload - as soon as onload fires, you go ahead and fetch some extra >components. Check google.com for an example of how a sprite image is requested onload. >This sprite image is not needed on the google.com homepage, but it is needed on the >consecutive search result page.
•Conditional preload - based on a user action you make an educated guess where the user >is headed next and preload accordingly. On search.yahoo.com you can see how some extra >components are requested after you start typing in the input box.
•Anticipated preload - preload in advance before launching a redesign. It often happens >after a redesign that you hear: "The new site is cool, but it's slower than before". Part >of the problem could be that the users were visiting your old site with a full cache, but >the new one is always an empty cache experience. You can mitigate this side effect by >preloading some components before you even launched the redesign. Your old site can use >the time the browser is idle and request images and scripts that will be used by the new >site
If you are using JQuery, then you can take a look at this: Preloading images with jQuery
Interesting concepts to improve download speed, perceived speed and actual speed:
7 techniques for faster JavaScript loading without compromising performance…
Make better use of caching
Download external scripts after visible content is loaded &
download multiple JavaScript in batch (asp.net/ajax)
Most principles explained are still generally applicable.