Steve Souders Even Faster Web Sites best practices for faster pages Disclaimer: This content does not necessarily reflect the opinions of my employer.

17% 83% iGoogle, primed cache The Importance of Frontend Performance 9%91% iGoogle, empty cache

Time Spent on the Frontend Empty CachePrimed Cache search.live.com/results67%0% en.wikipedia.org/wiki94%91%

The Performance Golden Rule 80-90% of the end-user response time is spent on the frontend. Start there. greater potential for improvement simpler proven to work

14 Rules 1.Make fewer HTTP requests 2.Use a CDN 3.Add an Expires header 4.Gzip components 5.Put stylesheets at the top 6.Put scripts at the bottom 7.Avoid CSS expressions 8.Make JS and CSS external 9.Reduce DNS lookups 10.Minify JS 11.Avoid redirects 12.Remove duplicate scripts 13.Configure ETags 14.Make AJAX cacheable

High Performance Web Sites YSlow

20% discount: vel08sthttp://conferences.oreilly.com/velocity/

Even Faster Web Sites 1.Split the initial payload 2.Load scripts without blocking 3.Don't scatter scripts 4.Split dominant content domains 5.Make static content cookie-free 6.Reduce cookie weight 7.Minify CSS 8.Optimize images 9.Use iframes sparingly 10.To www or not to www

AOL eBay Facebook MySpace Wikipedia Yahoo! YouTube Why focus on JavaScript?

Scripts Block blocks parallel downloads and rendering What's "Cuzillion"?

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

Split the Initial Payload: Facebook 43 external scripts, 550K uncompressed 9% of functionality is used before onload

Unexecuted Payload functions not used before onload search.live.com/results76% en.wikipedia.org/wiki68% % avg

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?

MSN 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) MSN.com: Parallel Scripts

Advanced Script Loading 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 Injection 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

Script in Iframe <iframe src='A.html' width=0 height=0 frameborder=0 id=frame1> 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');

Script DOM Element 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

Script Defer only supported in IE script and main page domains can differ no need to refactor JavaScript

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

Browser Busy Indicators

status bar progress bar logocursor block render block onload normal Script Src FFIE,FF FFIE,FF XHR Eval no XHR Injection no Script in Iframe IE,FFFFIE,FFFFnoIE,FF Script DOM Element FF noFF Script Defer FF IE,FF document.write Script Tag FFIE,FF FFIE,FF good to show busy indicators when the user needs feedback bad when downloading in the background

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

Summary of Traits || down- loads domains can differ existing scripts browser busy ensures order size (bytes) normal Script Src noyes IE,FF ~50 XHR Eval IE,FFno ~500 XHR Injection IE,FFnoyesno ~500 Script in Iframe IE,FFno IE,FFno~50 Script DOM Element IE,FFyes FF ~200 Script Defer IEyes IE,FFIE~50 document.write Script Tag IE * yes IE,FFIE~100 * Only other document.write scripts are downloaded in parallel (in the same script block).

and the winner is...

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?

Inline Scripts Block Rendering long executing inline scripts block rendering of the entire page workarounds: initiate execution with setTimeout move JavaScript to external script with advanced downloading techniques

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

eBay MSN MySpace Wikipedia Examples of Scattered Scripts

Don't Scatter Scripts remember inline scripts carry a cost avoid long-executing inline scripts don't put inline scripts between stylesheets and other resources

Takeaways focus on the frontend run YSlow: Velocity: register before May 5 this year's focus: JavaScript Split the Initial Payload Load Scripts without Blocking Don't Scatter Scripts speed matters you CAN make your site even faster!

Steve Souders