even faster web sites at the ajax experience
DESCRIPTION
Even Faster Web Sites covering loading scripts without blocking, coupling asynchronous scripts, and flushing the document early.TRANSCRIPT
17%
83%
iGoogle, primed cache
the importance of frontend performance
9% 91%
iGoogle, empty cache
14 RULES
1. MAKE FEWER HTTP REQUESTS
2. USE A CDN3. ADD AN EXPIRES HEADER4. GZIP COMPONENTS5. PUT STYLESHEETS AT THE
TOP6. PUT SCRIPTS AT THE
BOTTOM7. AVOID CSS EXPRESSIONS8. MAKE JS AND CSS
EXTERNAL9. REDUCE DNS LOOKUPS10.MINIFY JS11.AVOID REDIRECTS12.REMOVE DUPLICATE
SCRIPTS13.CONFIGURE ETAGS14.MAKE AJAX CACHEABLE
web performance guy
Even Faster Web SitesSplitting the initial payloadLoading scripts without blockingCoupling asynchronous scriptsPositioning inline scriptsSharding dominant domainsFlushing the document earlyUsing iframes sparinglySimplifying CSS Selectors
Understanding Ajax performance..........Doug CrockfordCreating responsive web apps............Ben Galbraith, Dion
AlmaerWriting efficient JavaScript.............Nicholas ZakasScaling with Comet.....................Dylan SchiemannGoing beyond gzipping...............Tony GentilcoreOptimizing images...................Stoyan Stefanov, Nicole
Sullivan
AOLeBayFacebookMySpaceWikipediaYahoo!
Why focus on JavaScript?
YouTube
scripts block
<script src="A.js"> blocks parallel downloads and rendering
7 secs: IE 8, FF 3.5, Chr 2, Saf 4
9 secs: IE 6-7, FF 3.0, Chr 1, Op 9-10, Saf 3
MSNScripts and other resources downloaded in parallel! How? Secret sauce?!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)
MSN.com: parallel scripts
Loading Scripts Without Blocking
XHR Eval
XHR Injection
Script in Iframe
Script DOM Element
Script Defer
document.write Script Tag
XHR Eval
script must have same domain as main page
must refactor script
var xhrObj = getXHRObject();xhrObj.onreadystatechange = function() { if ( xhrObj.readyState != 4 ) return; eval(xhrObj.responseText); };xhrObj.open('GET', 'A.js', true);xhrObj.send('');
XHR Injectionvar 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
Script in Iframe<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 pagewindow.frames[0].createNewDiv();
// access main page from iframeparent.document.createElement('div');
Script DOM Elementvar se = document.createElement('script');se.src = 'http://anydomain.com/A.js';document.getElementsByTagName('head')[0].appendChild(se);
script and main page domains can differ
no need to refactor JavaScript
<script defer src='A.js'></script>
supported in IE and FF 3.1+
script and main page domains can differ
no need to refactor JavaScript
Script Defer
document.write("<script type='text/javascript' src='A.js'> <\/script>");
parallelization only works in IE
parallel downloads for scripts, nothing else
all document.writes must be in same script block
document.write Script Tag
browser busy indicators
*Only other document.write scripts are downloaded in parallel (in the same script block).
Load Scripts Without Blocking
XHR EvalXHR InjectionScript in iframeScript DOM ElementScript Defer
Script DOM ElementScript Defer
Script DOM Element
Script DOM Element (FF)Script Defer (IE)
XHR EvalXHR InjectionScript in iframeScript DOM Element (IE)
XHR InjectionXHR EvalScript DOM Element (IE)
Managed XHR InjectionManaged XHR EvalScript DOM Element
Managed XHR InjectionManaged XHR Eval
Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection
Script DOM Element (FF)Script Defer (IE)Managed XHR EvalManaged XHR Injection
different domains same domains
no order
preserve order
no order
no busyshow busy
show busyno busy
preserve order
and the winner is...
menu.jsimage.gif
asynchronous JS example: menu.js
<script type="text/javascript">var domscript = document.createElement('script');domscript.src = "menu.js"; document.getElementsByTagName('head')
[0].appendChild(domscript);
var aExamples = [ ['couple-normal.php', 'Normal Script Src'], ['couple-xhr-eval.php', 'XHR Eval'], ... ['managed-xhr.php', 'Managed XHR'] ];
function init() { EFWS.Menu.createMenu('examplesbtn', aExamples);}
init();</script>
script DOM element approach
before
after
menu.jsimage.gif
menu.jsimage.gif
*Only other document.write scripts are downloaded in parallel (in the same script block).
!IE
Loading Scripts Without Blocking
what about
inlined code that depends on the script?
coupling techniques
hardcoded callback
window onload
timer
degrading script tags
script onload
John Resig's degrading script tags
<script src="menu-degrading.js" type="text/javascript">var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];
function init() { EFWS.Menu.createMenu('examplesbtn', aExamples);}
init();</script>
at the end of menu-degrading.js:var scripts =
document.getElementsByTagName("script");var cntr = scripts.length;while ( cntr ) { var curScript = scripts[cntr-1]; if (curScript.src.indexOf("menu-degrading.js") != -1) { eval( curScript.innerHTML ); break; } cntr--;}
http://ejohn.org/blog/degrading-script-tags/
cleanerclearersafer – inlined code not called if script
failsno browser supports it
technique 4: degrading script tags
<script type="text/javascript">var aExamples = [['couple-normal.php', 'Normal Script Src'],...];
function init() { EFWS.Menu.createMenu('examplesbtn', aExamples);}
var domscript = document.createElement('script');domscript.src = "menu-degrading.js";if ( -1 != navigator.userAgent.indexOf("Opera") ) { domscript.innerHTML = "init();";}else { domscript.text = "init();";}document.getElementsByTagName('head')[0].appendChild(domscript);</script>
elegant, flexible (cool!)not well knowndoesn't work for 3rd party scripts
(unless...)
technique 5: script onload<script type="text/javascript">var aExamples = [['couple-normal.php', 'Normal Script Src'], ...];
function init() { EFWS.Menu.createMenu('examplesbtn', aExamples);}
var domscript = document.createElement('script');domscript.src = "menu.js";
domscript.onloadDone = false;domscript.onload = function() { if ( ! domscript.onloadDone ) { init(); } domscript.onloadDone = true; };domscript.onreadystatechange = function() { if ( "loaded" === domscript.readyState ) { if ( ! domscript.onloadDone ) { init(); } domscript.onloadDone = true; }}
document.getElementsByTagName('head')[0].appendChild(domscript);</script>
pretty nice, medium complexitymenu.jsimage.gif
asynchronous loading & coupling
async technique: Script DOM Elementeasy, cross-browserdoesn't ensure script order
coupling technique: script onloadfairly easy, cross-browserensures execution order for external
script and inlined code
multiple interdependent external and inline scripts:much more complex (see hidden slides)concatenate your external scripts into
one!
flushing the document early
gotchas:PHP output_buffering – ob_flush()Transfer-Encoding: chunkedgzip – Apache's DeflateBufferSize before
2.2.8proxies and anti-virus softwarebrowsers – Safari (1K), Chrome (2K)
other languages: $| or FileHandle autoflush (Perl), flush
(Python), ios.flush (Ruby)
htmlimageimagescript
htmlimageimagescript call PHP's flush()
flushing and domain blocking
you might need to move flushed resources to a domain different from the HTML dochtml
imageimagescript
htmlimageimagescript
blocked by HTML document
different domains
successful flushing
Google Search
external resource downloaded earlycontent visible to the user
googleimageimagescriptimage204
http://www.google.com/images/nav_logo4.png
YSlow
Page Speed
Pagetest VRTA neXpert
combine JS & CSS X X Xuse CSS sprites X Xuse a CDN X Xset Expires in the future
X X X X X
gzip text responses X X X X Xput CSS at the top X Xput JS at the bottom Xavoid CSS expressions X Xmake JS & CSS externalreduce DNS lookups X Xminify JS X X Xavoid redirects X X X Xremove dupe scripts Xremove ETags X X X
performance analyzers (HPWS)
performance analyzers (EFWS)YSlo
wPage
SpeedPagetest VRTA neXper
tdon't block UI thread
split JS payload Xload scripts async X
inline JS b4 stylesheet Xwrite efficient JS
min. uncompressed size
optimize images X Xshard domains X X
flush the documentavoid iframes
simplify CSS selectors X X
performance analyzers (other)YSlo
wPage
SpeedPagetest VRTA neXper
tuse persistent conns X X Xreduce cookies 2.0 X X Xavoid net congestion Xincrease MTU, TCP win
X
avoid server congestion
X
remove unused CSS Xspecify image dims Xuse GET for Ajax 2.0reduce DOM elements
2.0
avoid 404 errors 2.0avoid Alpha filters 2.0don't scale images 2.0 Xoptimize favicon 2.0
focus on the frontend
run YSlow (http://developer.yahoo.com/yslow)
and Page Speed! (http://code.google.com/speed/page-speed/)
speed matters
takeaways
Bing:
Yahoo:
Google:
AOL:
Shopzilla:
1 http://en.oreilly.com/velocity2009/public/schedule/detail/8523 2 http://www.slideshare.net/stoyan/yslow-20-presentation3 http://en.oreilly.com/velocity2009/public/schedule/detail/75794 http://en.oreilly.com/velocity2009/public/schedule/detail/7709
+2000 ms -4.3% revenue/user1
+400 ms -5-9% full-page traffic2
+400 ms -0.59% searches/user1
fastest users +50% page views3
-5000 ms +7-12% revenue4
impact on revenue
hardware – reduced loadShopzilla – 50% fewer servers
bandwidth – reduced response size
http://billwscott.com/share/presentations/2008/stanford/HPWP-RealWorld.pdf
cost savings
if you want better user experience more revenue reduced operating costs
the strategy is clear
Even Faster Web Sites
Steve [email protected]
http://stevesouders.com/docs/tae-20090914.ppt
book signing immediately 3:30-3:50