Post on 26-Mar-2015
transcript
Building Fast 3rd-Party Webapps
O'Reilly VelocityWeb Performance and Operations Conference
24 June 2010
marcus@meebo-inc.commartinh@meebo-inc.com
Lessons learned from the Meebo Bar
Martin Hunt and Marcus Westin
The Meebo BarA customizable site bar with real-time social interaction
Meebo Bar, a 3rd Party Webapp
How do we make it run fast?
Loads on every pageInteracts with the page
JavaScript, CSS, Images & HTML
How do we make it respectful?
3rd Party WebappsThe Challenge
Do• Load lots of features• Load features fast
Without• Blocking rendering or onload• Affecting User Experience
How?
3rd Party Webapps: How?
• How to initialize a webappAsynchronous & non-blockingo
• Defer ExecutionMinimize impact when loading
• CSS and ImagesCrush, Combine, Avoid
• Perceived PerformanceTesting and psychology
Tools Techniques
Meebo Bar embed code
• executes in ~10mso no blocking network requestso no dependency on our server
• less than 1200 characters• gzips to about 700 bytes• embedded directly in page HTML or JS• executes even if our servers are not reachable
Initializing 3rd Party Webapps
Script Tagappend a script tag using JavaScript to the head of the documentCommonly accepted, but...
Inline JS <script src="">easy for publishers to addblocks the page in all browsers
XMLHttpRequestsAsynchronous, non-blockingsame-domain in most browsers
Iframe <iframe src="">load an HTML file in an iframeRequires HTML file on the hosting site
Accepted script loading code
var head = document.getElementsByTagName('head')[0],el = document.createElement('script');el.src = "http://www.myDom.ain/myScript.js"; head.appendChild(el);
good: cross domain (we're 3rd party content!)good: doesn't block network traffic
Don't 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 browsers
are there alternative nonblocking methods?
Iframed JS
1. 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 solution var iframe = document.createElement('iframe'), doc = iframe.contentWindow.document; doc.open().write('<body onload="appendScriptTag()">') doc.close()
More About Iframes
iframe creation overhead?
Creating one DOM nodeo Chrome < 1mso Firefox, Safari ~1mso IE ~5ms
Sandboxed 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 Execution
Lots of stuff happens in a browser while loading a page
Then, relatively little happens... Take advantage of this!
Defer Execution ExampleIn-page sharing
Defer Execution ExampleIn-page sharing
Defer Execution ExampleIn-page sharing
Defer Execution ExampleIn-page sharing
Naive implementation
function makeSharable(elements) { for (var i=0; i < elements.length; i++) { var element = elements[i]; var metadata = lookupMetadata(element); element.on('mousedown', startDrag, metadata); }}function lookupMetadata(el) { do { inspectElement(el) } while(el = el.parentNode)}
O(N)
O(M)
O(N*M)
Deferred implementation
function initShare() { document.on('mousedown', function(e) { 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); });}
O(1)
Page finishes loading
Modularize & Lazy Loadusers don't need all features immediately
1-1 Messagingconnect to all the
IM networks Broadcastingpublishers send new
content to usersSocial Networkingreceive updates aboutyour friends' activities Sharing
share site content to Facebook, Twitter, Buzz,
and other sitesSite Widgetssite-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 Images
Spriting and preloading is hardStill creates additional HTTP requestsDifficult to automate
Embed images into CSS insteadDataURIs and MHTML filesDetails on the Meebo devblog (http://mee.bo/cssimages)
Use Vector Graphics
Vector graphics are supported in all major browsers
• Firefox 3+• Opera 9.5+• IE 6+• Safari 3+• Chrome
Without images
With images
Tools - use them!
Preprocess if possible• if multiple clients are
doing the exact same task, run it on the server
• generate content offline
Compilers• Closure Compiler
Profilers• DynaTrace (IE)• Speed tracer (Chrome)• Firebug (FF)• Safari 5/WebKit
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!
Questions?marcus@meebo-inc.commartinh@meebo-inc.com
Highlights
• Always compress and minify content• Use an IFrame to load the main script payload• Defer execution until needed• Defer content download until needed• Remove HTTP requests by combining content
o Embed images into CSSo Use vector graphics