Steve Souders Life's too short, write fast code part 1 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% April 2008

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

June 22-24, 2009

High Performance Web Sites, Vol 2 1.Split the initial payload 2.Load scripts without blocking 3.Don't scatter inline scripts 4.Split dominant 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 } part 1

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

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

JavaScript Functions Executed before onload % search.live.com/results17K24% en.wikipedia.org/wiki114K32% % avg 252K avg Initial Payload and Execution

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? 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

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 (just landed in FF 3.1) script and main page domains can differ no need to refactor JavaScript

document.write Script Tag document.write("<scr" + "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... XHR Eval XHR Injection Script in iframe Script DOM Element Script Defer Script DOM Element Script Defer Script DOM Element Script DOM Element (FF) Script Defer (IE) XHR Eval XHR Injection Script in iframe Script DOM Element (IE) XHR Injection XHR Eval Script DOM Element (IE) Managed XHR Injection Managed XHR Eval Script DOM Element Managed XHR Injection Managed XHR Eval Script DOM Element (FF) Script Defer (IE) Managed XHR Eval Managed XHR Injection Script DOM Element (FF) Script Defer (IE) Managed XHR Eval Managed XHR Injection different domains same domains no order preserve orderno order no busy show busy no busy preserve order

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 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)

Inline Scripts after Stylesheets Block Downloading Firefox 3 and IE download stylesheets in parallel...unless the stylesheet is followed by an inline script best to move inline scripts above stylesheets or below other resources use Link,

eBay MSN MySpace Wikipedia Examples of Scattered Scripts

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

Announcement 1: UA Profiler tracks browser performance traits go to the test page your browser automatically walks through the tests (requires JS) results recorded and shared publicly currently 2K+ tests, 1K+ unique testers, 100+ browsers help out by running the test!

Measuring Performance Episodes dev boxsynthetic testing bucket testing real user data Hammerhead

Announcement 2: Hammerhead "moving performance testing upstream" Firebug extension load M URLs N times, empty & primed cache record average & median time add'l features: export data load time measurement modal cache clearing combine with bandwidth throttler

Facebook Performance Analysis the good –CDN (Akamai) –future Expires header (~10 days) –gzip turned on –stylesheets at the top (pretty much) –few CSS expressions (4) –JavaScript is minified –no redirects –few ETags (only profile photos)

1.move js below css 2.shard across 2 domains 3.combine scripts, load async, move lower 4.sprite CSS background images 5.prefetch resources for next page Welcome

Home ~150 requests ~1M JavaScript (uncompr) ~300K CSS (uncompr)

Home 1.move js below css 2.combine stylesheets 3.combine scripts, load async, move lower 4.sprite CSS background images!! 5.reduce size of JS – 85% not used by onload 6.reduce size of CSS – 81% (240K) not used by onload 7.optimize images – 44% (97K) lossless (smushit.com) 8.reduce DNS lookups – 15 domains! 9.remove ETags on profile photos

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 life's too short, write fast code

Steve Souders