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Even Faster Web Sites best practices for faster pages

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Presentation on theme: "Even Faster Web Sites best practices for faster pages"— Presentation transcript:

1 Even Faster Web Sites best practices for faster pages
Permission to use photo given by Amnemona: Steve Souders Disclaimer: This content does not necessarily reflect the opinions of my employer.

2 The Importance of Frontend Performance
9% 91% 17% 83% iGoogle, primed cache Data source: Steve Souders Tested on IE6 on Comcast cable modem (~5 mbps) medium powered PC, April 2008. iGoogle, empty cache

3 Time Spent on the Frontend
Empty Cache Primed Cache 97% 95% 81% 47% 0% search.live.com/results 67% 98% 94% en.wikipedia.org/wiki 91% 96% Ten top sites according to Alexa.com. Data source: Steve Souders Tested on IE6 on Comcast cable modem (~5 mbps) medium powered PC, April 2008. For Google and Live Search there are so few components (2-4) and they're mostly cacheable so the HTML document is a bigger percentage.

4 The Performance Golden Rule
80-90% of the end-user response time is spent on the frontend. Start there. greater potential for improvement simpler If you could cut performance in half, FE changes would be 40-45%, while BE would be only 5-10%. BE changes are typically more complex: rearchitecture, optimize code, add/modify hw, distribute databases, etc. FE is simpler: change web server config, place scripts and stylesheets differently in the page, combine requests, etc. I’ve worked with dev teams to cut response times on 50 properties, often by 25% or more. And feedback from other companies is similar. Permission to use photo given by Technicolor: proven to work

5 14 Rules Make fewer HTTP requests Use a CDN Add an Expires header
Gzip components Put stylesheets at the top Put scripts at the bottom Avoid CSS expressions Make JS and CSS external Reduce DNS lookups Minify JS Avoid redirects Remove duplicate scripts Configure ETags Make AJAX cacheable photo courtesy of Vicki & Chuck Rogers:

6 YSlow High Performance Web Sites

7 June 22-24, 2009

8 High Performance Web Sites, Vol 2
Split the initial payload Load scripts without blocking Don't scatter inline scripts Split dominant domains Make static content cookie-free Reduce cookie weight Minify CSS Optimize images Use iframes sparingly To www or not to www

9 Why focus on JavaScript?
Yahoo! YouTube AOL Wikipedia eBay Facebook MySpace Data Source: Steve Souders aol 76% ebay 45% facebook 41% google 42% live search 9% msn 37% myspace 37% yahoo 45% youtube 60% wikipedia 26% average 42%

10 Scripts Block <script src="A.js"> blocks parallel downloads and rendering What's "Cuzillion"?

11 Cuzillion 'cuz there are a zillion pages to check
a tool for quickly constructing web pages to see how components interact Open Source

12 Initial Payload and Execution
JavaScript Functions Executed before onload 115K 30% 183K 44% 1088K 9% 15K 45% search.live.com/results 17K 24% 131K 31% 297K 18% en.wikipedia.org/wiki 114K 32% 321K 13% 240K Data source: Steve Souders 252K avg 26% avg

13 Split the initial payload
split your JavaScript between what's needed to render the page and everything else load "everything else" after the page is rendered separate manually (Firebug); tools needed to automate this (Doloto from Microsoft) load scripts without blocking – how? Permission to use photo given by Brian.H -

14 MSN.com: Parallel Scripts
Scripts and other resources downloaded in parallel! How? var p= g.getElementsByTagName("HEAD")[0]; var c=g.createElement("script"); c.type="text/javascript"; c.onreadystatechange=n; c.onerror=c.onload=k; c.src=e; p.appendChild(c) Of the ten top sites, MSN.com (Script DOM Element), Live Search (Script in Iframe), and Yahoo (Script DOM Element) use advanced script loading techniques.

15 Advanced Script Loading
XHR Eval XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag All of these allow for parallel downloads, but none of them allow for parallel JS execution – that's not possible (currently, WebKit is doing some stuff on that).

16 XHR Eval script must have same domain as main page
var xhrObj = getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; eval(xhrObj.responseText); }; xhrObj.open('GET', 'A.js', true); xhrObj.send(''); script must have same domain as main page must refactor script

17 XHR Injection script must have same domain as main page
var xhrObj = getXHRObject(); xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; var se=document.createElement('script'); document.getElementsByTagName('head') [0].appendChild(se); se.text = xhrObj.responseText; }; xhrObj.open('GET', 'A.js', true); xhrObj.send(''); script must have same domain as main page

18 Script in Iframe iframe must have same domain as main page
<iframe src='A.html' width=0 height=0 frameborder=0 id=frame1></iframe> iframe must have same domain as main page must refactor script: // access iframe from main page window.frames[0].createNewDiv(); // access main page from iframe parent.document.createElement('div');

19 Script DOM Element script and main page domains can differ
var se = document.createElement('script'); se.src = ' document.getElementsByTagName('head') [0].appendChild(se); script and main page domains can differ no need to refactor JavaScript

20 Script Defer only supported in IE
<script defer src='A.js'></script> only supported in IE script and main page domains can differ no need to refactor JavaScript

21 document.write Script Tag
"ipt type='text/javascript' src='A.js'>" + "</scri" + "ipt>"); parallelization only works in IE parallel downloads for scripts, nothing else all document.writes must be in same script block

22 Browser Busy Indicators
Audio (IE "click") is another busy indicator. Delayed rendering and delayed onload ("done") are other busy indicators. Sometimes busy indicators are bad, sometimes good.

23 Browser Busy Indicators
status bar progress logo cursor block render onload normal Script Src FF IE,FF XHR Eval no XHR Injection Script in Iframe Script DOM Element Script Defer document.write Script Tag Data source: Steve Souders Audio (IE "click") is another busy indicator. Delayed rendering and delayed onload ("done") are other busy indicators. Sometimes busy indicators are bad, sometimes good. good to show busy indicators when the user needs feedback bad when downloading in the background

24 Ensure/Avoid Ordered Execution
Ensure scripts execute in order: necessary when scripts have dependencies IE: FF: Avoid scripts executing in order: faster – first script back is executed immediately

25 Summary of Traits normal Script Src XHR Eval XHR Injection
|| down-loads domains can differ existing scripts browser busy ensures order size (bytes) normal Script Src no yes IE,FF ~50 XHR Eval ~500 XHR Injection Script in Iframe Script DOM Element FF ~200 Script Defer IE document.write Script Tag IE* ~100 Data source: Steve Souders *Only other document.write scripts are downloaded in parallel (in the same script block).

26 and the winner is... I'll do JavaScript and PHP implementations of this logic soon.

27 Load Scripts without Blocking
don't let scripts block other downloads you can still control execution order, busy indicators, and onload event What about inline scripts? Permission to use photo given by Reciprocity:

28 Inline Scripts Block long executing inline scripts block rendering and downloads workarounds: initiate execution with setTimeout (>250 for FF, nglayout.initialpaint.delay) move JavaScript to external script with advanced downloading techniques use Defer attribute (IE only)

29 Inline Scripts after Stylesheets Block Downloading
Firefox blocks parallel downloads when downloading stylesheets IE doesn't... ...unless the stylesheet is followed by an inline script best to move inline scripts above stylesheets or below other resources use Link, Joseph Smarr from Plaxo advocates interspersing setTimeout through JavaScript threads every n00 ms.

30 Examples of Scattered Scripts
Wikipedia MySpace eBay MSN Data source: Steve Souders

31 Don't Scatter Inline Scripts
remember inline scripts carry a cost avoid long-executing inline scripts don't put inline scripts between stylesheets and other resources Permission to use photo given by _iosonoshuo_:

32 Takeaways focus on the frontend
run YSlow: this year's focus: JavaScript Split the Initial Payload Load Scripts without Blocking Don't Scatter Inline Scripts speed matters you CAN make your site even faster!

33 Announcement 1: HTTPWatch for FF
previously IE only Firefox private beta now Firebug 1.05 Net Panel buggy

34 Announcement 2: Firebug Lite 1.2
console.log Inspect DOM and CSS

35 Announcement 3: Mozilla & Firebug
John Resig, Rob Campbell, Jan Odvarko Firebug Working Group stability, performance, bug fixes

36 Steve Souders souders@google.com http://stevesouders.com/
"thank you" by nj dodge: Steve Souders


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