Hiện tại, thế giới Internet đã thay đổi, trở nên quan trọng hơn và nhiều giá trị nội dung hơn, giao diện các website trở nên đẹp và tiện dụng hơn và hiển nhiên các trang web cũng cần nhiều thời gian hơn để tải về. Nhưng hầu hết các khách truy cập đều không muốn sự chờ đợi này, đây cũng là vấn đề đau đầu với tất cả các nhà phát triển web. Bài viết này hướng dẫn bạn một trong nhiều cách để rút ngắn thời gian tải trang web, đó là thiết lập thời hạn của các tệp tin CSS và JavaScript, đồng thời nén mã nguồn JavaScript, CSS lại trước khi trả về trình duyệt.

Vui lòng vào trang chi tiết để xem hướng dẫn đầy đủ và xem thêm các bài viết tối ưu khác:

- Các thủ thuật JavaScript và jQuery hữu ích
- Vài giải pháp cơ bản để tăng tốc JavaScript
- Vài hướng dẫn JavaScript cơ bản để tối ưu hóa hiệu suất trang web

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The landscape of the internet has changed a great deal over the years. Websites are no longer static and lifeless, they have become dynamic and interactive. A consequence of this is that the size of modern websites has increased significantly. This poses a couple of important issues:

1. It takes more time for webpages to be downloaded by client browsers.
2. Average website bandwidth usage has increased.

Most internet surfers won't wait 30 seconds for a page to load in its entirety, they'll simply move on to something else. Also, if you own or manage an even moderately busy website you will know just how much bandwidth is worth. It is a precious commodity that can increase the figures on your monthly hosting bill. As a result of this, a lot of emphasis is now being placed on website optimization.

Yahoo has published a set of rules which outlines some of the methods that can be employed to make your website as lean and fast as possible. One of the methods suggested is to compress and minify external CSS and JavaScript files. Some PHP frameworks employ some form of optimization of these files and if you have control over your server you can always install mod_gzip which would handle compression of these files. If you are not using a PHP framework or you use a shared hosting plan (most of which won't allow you to use mod_gzip because it can be a CPU hog) then read on.

First off, we will create a .htaccess file in which we will put our rewrite rules:

IndexIgnore *

<IfModule mod_rewrite.c>
	RewriteEngine on
	RewriteRule ^(.*\.((js)|(css)))$ optimizer.php?file=$1
</IfModule>

Place a copy of this file in your /js and your /css folders. The first line really has nothing to with our optimization, all it does is it prevents listing of the contents of the directory when someone navigates to http://www.yourdomain.com/js or http://www.yourdomain.com/css. Not necessary but good practice. The next few lines redirects incoming requests to the file optimizer.php if the file extension is .js or .css and passes the filename to it as a query string. Next, we'll create a file called optimizer.php:

<?php
if(!isset($_GET['file'])) die('Invalid parameter!');

$file = file_get_contents($_GET['file']);
$file = preg_replace("/((?:\/\*(?:[^*]|(?:\*+[^*\/]))*\*+\/)|(?:\/\/.*))/", "", $file);

header("Expires: Fri, 21 Dec 2012 00:00:00 GMT");
header("Content-type: application/x-javascript");
ob_start("ob_gzhandler");

echo $file;
ob_flush();
flush();
?>

This file should also be placed in both the /css and /js folders. What this script does is it grabs the filename from the $_GET array, reads the contents of the file into a variable, strips the file of all comments, sends content type and expires headers to the browser, compresses the contents of the variable (via output buffering) and sends the optimized CSS or JavaScript back to the browser. Simple and straightforward.

This method is a simple way to optimize your external .js and .css files when you don't have access to better(?) methods. The only issue I have noted so far with this method is that it will mess up the minified version of the jQuery library which really isn't an issue since its already minified. If you are using the minified version of jQuery on your website simply use this code in your optimize.php file instead:

<?php
if(!isset($_GET['file'])) die('Invalid parameter!');

$file = file_get_contents($_GET['file']);
$jqueryFile = 'name_of_your-jquery_file';

if($file!=$jqueryFile) $file = preg_replace("/((?:\/\*(?:[^*]|(?:\*+[^*\/]))*\*+\/)|(?:\/\/.*))/", "", $file);

header("Expires: Fri, 21 Dec 2012 00:00:00 GMT");
header("Content-type: application/x-javascript");
ob_start("ob_gzhandler");

echo $file;
ob_flush();
flush();
?>

Now go optimize your stylesheets and JavaScripts and make your users happier!

Footnote #1: This implementation will obviously only work on an apache server as a .htaccess file is used.

Footnote #2: The code used in this post is simply a proof of concept. Little or no attention was paid to security. In an actual implementation of this technique you would need to ensure that this script is as secure as possible.

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bởi Web Design Dubai, 04/11/2010 02:11 PM
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I had issues with your website on my browser and had to refresh the page a couple of times, I'm using an older version of Firefox. I enjoyed the articles and comments and will be back!

SEO in Dubai | Online Marketing Services

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