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Front end optimization -Abhishek Anand Web Engineering, Digital Centre of Excellence, HCL Technologies
Why should we optimize frontend? 80% of the end-user response time is spent on the front-end. Frontend optimization can cut off 25% to 50% of the page load time. Page load times are important. Amazon insiders estimate that every 100 ms increase in latency costs Amazon roughly %1 of profit. Visitors hate slow sites, so dont make them wait.
When to start frontend optimization? Right from the start of a project Image optimization and creating sprites for image.
Image optimization Progressive JPEG for large images with multiple colors, for anything with complex gradients (e.g., a photo). PNG if you need transparency, for small and simple image (e.g., icons) Dont Scale Images in HTML
Minimize HTTP Requests Combine CSS & JS into as few files as possible. /admin/settings/performance -“Optimize CSS files” and “Optimize JS files” from performance page: Create sprite images for background Images. use the CSS background-image and background-position properties to display the desired image segment.
Minimize HTTP Requests Inline images use the data: URL scheme to embed the image data in the actual page http://drupal.org/project/css_emimage Avoid Redirects Use GET for AJAX Requests
CSS Cleanup you can strip it out by finding/adding this function in your themes template.php file: phptemplate_preprocess_page Use Google page speed to find unused CSS files
Split Components Across Domains Use CDN http://drupal.org/project/cdn Most browsers only download two resources from one domain at a time (only one at a time for JS). Spreading static resources (like images, CSS, and JS) across couple of sub-domains will allow browsers to download things, 2 at a time, from each domain simultaneously.
Setting up cookie domain A domain that sets a cookie is considered a “cookie enabled domain” by whatever requests it. Disable cookies on static domains. In settings.php uncomment this line and put your domain in like this: $cookie_domain = ‘example.com;
Avoid CSS Expressions CSS expressions are a powerful (but dangerous) way to set CSS properties dynamically background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );
Reduce DNS Lookups DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname
No 404s HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit. Avoid Empty Image src
Avoid Filters The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7. The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded. It also increases memory consumption and is applied per element, not per image, so the problem is multiplied
Preload Components Unconditional preload - as soon as onload fires, you go ahead and fetch some extra components. Conditional preload - based on a user action you make a guess where the user is headed next and preload accordingly. Anticipated preload - preload in advance before launching a redesign.