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Speed is Essential for a Great Web Experience (Canvas Conf Version)
Our perception of response time
Instant Seamless Yawn! 100ms 1s 10s 3s - Recommended 7s - Fortune 500 Load Time Average (2010) Response Time in Man-computer Conversational Transactions Robert B. Miller, 1968
80% plus of page load
time is on front-end Backend news.bbc.co.uk Frontend ebay.co.uk debenhams.co.uk direct.gov.uk amazon.co.uk mumsnet.com guardian.co.uk 0 1.25 2.5 3.75 5 Measured on residential ADSL line using Chrome 19
Bandwidth (often) isn’t the bottleneck
2.0 1.5 1.0 0.5 0s 5s 10s news.bbc.co.uk tested via webpagetest.org throttled at 1.5Mbps (bursts over 1.5Mbps are artefact of testing)
Minimum round trips to download
a file (TCP Segments) 285kB 214kB 143kB 71kB Size 1 2 3 4 5 6 7 8 9 10 11 Round Trips TCP and the Lower Bound of Web Performance John Rauser
Get the <head> straight <!doctype
html> <html> <head> CSS before JS <meta charset="utf-8"> Ideally one file* <title>This is my title<title> <link rel="stylesheet" href="styles.css" type="text/css" /> <script src="script.js"></script> . . Only JS needed . during page load </head> * Bryan and Stephanie Rieger’s major and minor breakpoint approach requires multiple CSS files
Load remaining Javascript late as
possible . . . <script src="restofscript.js"></script> </body> </html> One file or many? (Depends on size) Could you defer some JS until after onload?
The Perils of Third Party
Javascript... “Virgin Media Broadband ISP Users Affected by Website Routing Woes” ISP Review, May 26, 2012 cg-global.maxymiser.com unreachable
Load Third Party scripts asynchronously
<script type="text/javascript"> function() { var js = document.createElement('script'); js.async = true; js.src = 'myscript.js'; var e = document.getElementsByTagName('script')[0]; e.parentNode.insertBefore(js, first); })(); </script> async attribute may be option but not supported by IE & Opera