Meebo performance ny_web_performance

Building Fast 3rd-Party Webapps Lessons learned from the Meebo Bar Marcus Westin follow me @marcuswestin (a replay from OReilly Velocity conference 24 June 2010) On Twitter: @marcuswestin and @mghunt

The Meebo BarA customizable site bar with real-time social interaction

Meebo Bar, a 3rd Party Webapp JavaScript, CSS, Images & HTML Interacts with the page Loads on every page How do we make it run fast?How do we make it respectful?

3rd Party Webapps The ChallengeDo Load lots of features Load features fastWithout Blocking rendering or onload Affecting User Experience How?

Meebo Bar embed codeexecutes in ~10ms no blocking network requests no dependency on our serverless than 1200 charactersgzips to about 700 bytesembedded directly in page HTML or JSexecutes even if our servers are not reachable

Initializing 3rd Party WebappsInline JS <script src=""> Iframe <iframe src="">easy for publishers to add load an HTML file in an iframeblocks the page in all Requires HTML file on thebrowsers hosting siteXMLHttpRequests Script TagAsynchronous, non- append a script tag usingblocking JavaScript to the head ofsame-domain in most the documentbrowsers Commonly accepted, but...

Accepted script loading codevar head = document.getElementsByTagName(head)[0],el = document.createElement(script);el.src = "http://www.myDom.ain/myScript.js"; head.appendChild(el);good: cross domain (were 3rd party content!)good: doesnt block network traffic

Dont block the page!Script Tag Appendcan block scripts in Firefox!blocks other scripts in Firefox scripts execute in order all scripts on the page block until the appended script downloads and executes (defer attribute supported in FF3.5+)blocks onload event in all browsersare there alternative nonblockingmethods?

Iframed JS1. Iframes load HTML, not JS2. Cross iframe communication is same-domain only (non- HTML5 browsers)3. Window onload event fires after all iframes load

Iframed JS - the solutionvar iframe = document.createElement(iframe), doc = iframe.contentWindow.document;doc.open().write( <script>function loadJS() { ... }</script> + <body onload="loadJS()">)doc.close()

More About Iframesiframe creation overhead? Creating one DOM node Chrome < 1ms Firefox, Safari ~1ms IE ~5msSandboxed JavaScript 3rd party code will not break webpage code Webpage code will not break 3rd party code!for (var i in x) {}

Defer Execution

Defer ExecutionLots of stuff happens in a browser while loading a pageThen, relatively little happens... Take advantage of this!

Defer Execution Example In-page sharing

Naive implementationfunction makeSharable(elements) { for (var i=0; i < elements.length; i++) { var element = elements[i]; var metadata = lookupMetadata(element); element.on(mousedown, startDrag, metadata); O(N) }}function lookupMetadata(el) { do { inspectElement(el) } while(el = el.parentNode) O(M)} O(N*M)

Deferred implementationfunction initShare() { document.on(mousedown, function(e) { O(1) var el = e.target || e.srcElement if (!el.getAttribute(meeboSharable)) { return; } var metadata = lookupMetadata(el); document.on(mousemove, handleDrag, metadata); document.on(mouseup, stopDrag, metadata); });} Page finishes loading

Modularize & Lazy Load users dont need all features immediately 1-1 Messaging connect to all the IM networks Broadcasting publishers send new content to users Social Networking receive updates about your friends activities Sharing share site content to Facebook, Twitter, Buzz, Site Widgets and other sites site-specific widgets:videos, menus, navigation tools, etc.

Modularize & Lazy Load Also applies to images and CSS! Careful: Loading images can create a lot of HTTP requests

Loading ImagesSpriting and preloading is hardStill creates additional HTTP requestsDifficult to automateEmbed images into CSS insteadDataURIs and MHTML filesDetails on the Meebo devblog (http://mee.bo/cssimages)

Use Vector GraphicsVector graphics are supportedin all major browsers Firefox 3+ Opera 9.5+ IE 6+ Safari 3+ Chrome

With imagesWithout images

Tools Techniques How to initialize a webapp Asynchronous & non-blocking Defer Execution Minimize impact when loading CSS and Images Crush, Combine, Avoid Perceived Performance Testing and psychology

Perceived Performance Quick loading content on a slow page appears to be the cause of the slow page Delaying interface drawing can look slow or broken Do not forget: Even asynchronous loading slows down a page. Keep payloads minimal and always monitor performance!

HighlightsAlways compress and minify contentUse an IFrame to load the main script payloadDefer execution until neededDefer content download until neededRemove HTTP requests by combining content Embed images into CSS Use vector graphics Questions? (+ ping me on twitter) @marcuswestin

We need better tools for measuringwebapp performance!Need to accurately determine theimpact of a webapp on a website

Browser CacheNew visitors dont have anything cached!Browsers can automatically clear cacheYahoo! YUI study: 40-60% of Yahoo!s users have an empty cache 20% of all page views have an empty cache

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Meebo performance ny_web_performance

by marcuswestin on Jan 05, 2011

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