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Frontend performance


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Frontend performance tips to boost your website load time

Frontend performance tips to boost your website load time

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  • 1. Frontend performance Best practices for speeding up your website
  • 2. Fact
    • Only 10–20% of the end user response time is spent downloading the HTML document. The other 80–90% is spent downloading all the components in the page.
    • If you want to dramatically reduce the response times of your web pages, you have to focus on the other 80–90% of the end user experience. What is that 80–90% spent on ?How can it be reduced?
  • 3. Best practices rules - Content
    • 1. Make fewer HTTP Requests
    • About HTTP requests
    • Content-Encoding (compression)
    • If-Modified-Since (conditional GET)
    • Expires: Wed, 05 Oct 2022 19:16:20 GMT-
    • Connection: Keep-Alive
    • Image Maps
    • CSS Sprits
    • Inline Images (data:URL/ fie_get_contents / encode data with MIME base64 )
    • e.g .cart { background-image: url(data:image/gif;base64, <?php echo base64_encode(file_get_contents(&quot;../images/cart.gif&quot;)) ?>);}
    • Combine JS and CSS
  • 4. Best practices rules - Content
    • 2. Reduce DNS lookups
    • DNS takes 20.120 milliseconds for DNS to lookup the IP address for a given hostname
    • ISP/browserscache DNS lookups
      • IE Cache expiration (30 mins)
      • FF Cache expiration (1 min)
      • IE keep-alive (1 min)
      • FF keep.alive (5 mins)
    • If cache is empty then number of DNS lookups = unique hostnames (URL, images, flash …etc)
    • Reduce number of unique hostnames reduces the amount of parallel downloads.
    • Reduce parallel downloads increase response time
    • TTL; DNS record returns from lookup TTL value which tells the client how long the record can be cached.
    • Use Keep-Alive to use existing connections and fewer domains
    • To flush DNS cache
    • Linux (/etc/init.d/nscd restart)
    • Mac OS X (dscacheutil --flushcache)
  • 5. Best practices rules - Content
    • 3. Avoid Redirects
    • HTTP/1.1 301 Moved Permanently
    • Location :
    • Content-Type: text/html
    • One of the most wastfull redirects is caused by the trailing slash
    • results in 301 respons to
    • But this is fixed in Apache by using Alias or mod_rewrite or DirectorySlash if you use Apache handlers.
    • See CNAME if you are using multiple HTTP servers with different names on same physical host (alias for pointing one domain to another)
  • 6. Best practices rules - Content
    • 4. Remove Duplicate Scripts
    • Unnecessary HTTP requests caused by extra js get requests increases load time.
    • One good way to overcome this is using a script management system in your template system
    • Drupal e.g.
    • In template .info file scripts[] = fly.js
    • In module drupal_add_js
  • 7. Best practices rules - Content
    • 5. Make Ajax cacheable
    • To improve performance, optimize Ajax responses and make them cacheable
    • Add Expires or Cache-Control headers
    • Gzip components
    • Reduce DNS Lookups
    • Minify JS
    • Avoid Redirects
    • Configure ETags
  • 8. Best practices rules - Content
    • 6. Post-load Components
    • Which component can wait to be loaded later.
    • YUI Image Loader which allows you to delay images
    • YUI Get Utility ; get JSand CSS on the fly
    • 7. Pre-load Components
    • Wait for idle browser state and request components that you might need in other pages
    • Types
    • Unconditional preload; once the page is loaded, fetch extra components
    • Conditional preload; user action based
    • Anticipated preload; preload in advance
  • 9. Best practices rules - Content
    • 7. Reduce number of DOM Elements
    • High number of DOM elements means that something should be improved with markup of page.
    • Nested Tables ? Divs to fix layout issues
    • YUI CSS utility which contains CSS reset.
    • To get number of DOM elements type in Firebug console
    • Document.getElementByTagName(‘*’).length
    • 8. Split components across domains
    • So you can maximize parallel downloads, make sure not to use 2-4 domains (DNS lookup)
    • Dynamic content on, static on,
  • 10. Best practices rules - Content
    • 9. Minimize number of iframes
    • Pros
    • Third party content
    • Security
    • Download scripts in parallel
    • Cons
    • Resources
    • Block page onload
    • Non-semantic (how document supposed to look rather than its structure)
  • 11. Best practices rules - Content
    • 10. No 404s
    • Extra HTTP requests
    • Alternatives ?
  • 12. Best practices rules - Server
    • 1. User CDN
    • Collection of web servers distributed across multiple locations to deliver content more efficiently to users
    • 2. Add an Expires or Cache-Control header
    • Static Content; never expire
    • Dynamic content; cache-control (conditional requests)
    • 3. Gzip components
    • Gzipping reduce response size by about %70 (Apache1.3 mod_gzip/ Apache2.x mod_deflate)
    • Server chooses what to gzip (html/xml/json) and what not to gzip (pdf/images)
  • 13. Best practices rules - Server
    • 4. Configure Entity Tags (ETags)
    • Mechanism that web servers and browsers use to determine whether the component/entity in the browser’s cache matches the one on the origin server (image/js file/css file).
    • Etags is a more flexible mechanism than last-modified date
    • Etag is a string identifying version of component
    • Last-modified: validate based on timestamp
    • Etag: ’ 10c23bs-4ab-45345f2a ’
    • Drowback of Etags is it typically constructed on a specific server hosting a site and wont match on another server
    • If you are not taking advatages, disable it from Apache config file because it increases the size of HTTP headers in response and requests.
    • FileETag none // in apache config files
  • 14. Best practices rules - Server
    • 5. Flush the Buffer Early
    • On page request the backend needs around 200-500ms to stitch together your HTML page, during this time the browser is idle.
    • In PHP you have function flush() which allows sending partically ready HTML to the browser while your backend is busy collection more component.
    • Best place to consider flush() is your HTML HEAD tag
    • 6. Use GET for Ajax requests
    • POST request happen in 2 steps: send headers, send data
    • GET request takes on TCP packet to send
    • 7. Avoid empty image scr
    • Read Empty Image src can destroy your site
  • 15. Best practices rules – Cookies
    • 1. Reduce cookie size
    • Eliminate unnecessary cookies
    • Apply cookies to domains NOT subdomains
    • Set Expires date
    • 2. Use cookie-free domains for components
    • When a browser request a static image and sends a cookie with the request, the server does not use that cookie, so its only no good for traffic, you should make static components cookie-free request
    • Create a subdomain to host all your static data, that way * uses the cookie
    • Omitting www from your domain oblige you to write cookies to *
    • So for better performance use www subdomain.
  • 16. Best practices rules - CSS
    • 1. Put CSS at top
    • Moving css to the head makes pages appear loading faster because the page is rendering progressively.
    • 2. Avoid CSS expressions
    • CSS expressions are used to set CSS properties dynamically
    • CSS Expressions accept JS expressions
    • Background-color: expression( (new Data()).getHours()%2 ? ‘red’ : ‘black’ );
    • Width: expression( document.body.clientWidth < 600 ? ‘600px’ : ‘auto’);
    • Drawbacks
    • Expressions evaluated on page render, resize, scroll, mouse over …etc.
    • Moving the mouse a little bit can generate more than 10,000 evaluation
    • To reduce CSS expressions evaluations user one-time
    • Background-color: expression(altBgColor(this));
    • <script>
    • Function altBgColor(element) {
    • = (new Data()).getHours()%2 ? ‘red’ : ‘black’ );
    • }
    • </script>
  • 17. Best practices rules - css
    • 3. Choose <link> over @import
    • 4. Avoid Filters
    • IE-Proprietary AlphaImageLoader and others increase memory consumption and its applied per element not per image.
    • Solve this and user
  • 18. Best practices rules - JS
    • 1. Put JS at the bottom
    • Scripts block parallel downloads
    • We cannot put document.write at the bottom
    • We can use DEFER attribute to indicate that the script does not contain document.write (FF don’ t support, IE does)
    • <script type=‘text/javascript’ src=‘ fly.js ’ defer= ‘ defer ’ ></script>
    • 2. Make Javascripts and CSS external
    • Using external files (not inline) of JS and CSS generally produces faster pages because JS and CSS are cached by the browser.
    • While inline JS and CSS are loaded on each page load
  • 19. Best practices rules - JS
    • 3. Minify JS and CSS
    • Minifying removes unnecessary characters to reduce size (remove all comments, white spaces)
    • Minifying tools JSMin and YUI compressor
    • 4. Remove Duplicate Scripts
    • Unnecessary HTTP requests caused by extra js get requests increases load time.
    • One good way to overcome this is using a script management system in your template system
    • 5. Minimize DOM Access
    • Accessing DOM elements with JS is slow
    • Read /
  • 20. Best practices rules - JS
    • 6. Develop smart event handles
    • Attaching too many event handles to DOM elements might make pages less responsive
    • Event delegation/bubbling is a bingo; whenever you do something to an element, the elements tell parent elements or a like elements about it
  • 21. Best practices rules - Images
    • 1. Optimize Images
    • Use PNGs rather than GIFs
    • Run pngcrush on all your PNGS /
    • Run jpegtran on all your JPEGs /
    • 2. Optimize CSS Sprits
    • Arrange sprites horizontally rather than vertically reduce small size file
    • Don’ t leave big gaps between image, this does not impact the file size, but requires less momory to decompress the image into a pixel map
    • 3. Don’ t scallimages in HTML
    • 4. Make favicon.ico small and cacheable
    • Under 1K
    • Imagemagick can help you create small favicons http://
  • 22. Best practices rules – Mobile
    • Keep components under 25k
    • iPhone wont cache components bigger that 25K
    • Performance Reasearch , Part 5: iPhone cacheability
    • 2. Pack components into multipart document
    • Packing components into multipart document is like an email with attachement, it helps fetching several components with one HTTP request.
  • 23. Thank you Alaa H Batayneh