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CSS properties play a vital role in the construction of web pages. These properties are dynamically set using CSS expressions. Ignored by other browsers, the expression method is supported in Internet Explorer. Frequent evaluation of expressions is a problem with using CSS properties. They are frequently evaluated during not only rendering and resizing but also scrolling of web pages. Even the mouse movement over the page can generate above 10,000 evaluations. It slows down the performance of websites.

Using one-time expressions is a means to cut down the number of evaluations of CSS expressions. The first time evaluation of the expression sets an explicit value to the style property. The CSS expression is replaced by the style property. Using event handlers is an alternative approach to set the style property dynamically and keep the performance of websites intact.

Using external files produces fast-loading pages as Javacript and CSS files are cacheable to the browsers. Using Javascript and CSS files if inlined in HTML documents reduces HTTP requests in number. Increase in the size of the HTML document is the only downside of this option. Frequency of using Javascript and CSS components in external files in keeping with the number of HTML documents is the key factor to ensure multiple views of pages at ease. Cacheable external files offer greater potentiality to boost website performance.

Besides deploying the JavaScript and CSS components in external files, inlining them in the front page of websites is another technique to keep the volume of HTTP request in check. Once the front page has loaded, subsequent pages in the browser’s cache will load faster. It improves the response times for end-users.

DNS stands for Domain Name System. It records hostnames relating to IP addresses much the same way as phonebooks keep record of people’s names relating to their phone numbers. On typing a site’s URL in your browser, a DNS resolver returns the IP address of that server. It takes DNS 20-120 milliseconds to search for the IP address of a given hostname. Only on completion of the DNS lookup, the browser can download something from the hostname.

Cacheable DNS lookups account for better performance of websites. The operating system’s DNS cache keeps the DNS information. Most browsers have caches of their own in distinction with that of operating systems. As long as the DNS information is in the browser’s cache, it does not trouble the operating system for the record. When there is no DNS information in the cache of both the browser and the operating system, the number of DNS lookups equals that of hostnames in the URL, script files, images, stylesheets and flash components of the webpage. The number of DNS lookups decreases with a decrease in the number of hostnames ensuring the fast loading of pages. It reduces the number of HTTP requests and improves the response time of servers as well.

I will share with you some more tips on how to boost website performance in my next blog…