Developing High Performance Web Apps - CodeMash 2011
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Developing High Performance Web Apps - CodeMash 2011

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Talk given at CodeMash 2011

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  • Accessing a DOM element always comes at a price. \nIt is not the same as accessing any other local or global variable in JavaScript.\n
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Developing High Performance Web Apps - CodeMash 2011 Presentation Transcript

  • 1. CODE MASH 2011 DEVELOPING HIGHPERFORMANCE WEB APPS Timothy Fisher Compuware January 14, 2011
  • 2. WHO AM I? Timothy Fisher Technical Consultant CTO Office - Emerging Technologies @tfisher tim.fisher@compuware.com www.timothyfisher.comDownload this presentation at: http://www.slideshare.net/timothyf
  • 3. AGENDA• Why Front-end Performance Matters• Optimize Page Load• Responsive Interfaces• Loading and Executing JavaScript• Data Access
  • 4. AGENDA• DOM Scripting• Tools• Performance Monitoring• QuestionsAn overview to spark thought and further investigation
  • 5. TRAIL BLAZERS• Steve Souders• Nicholas Zakas• Stoyan Stefanov• Patrick Meenan• Sergey Chernyshev
  • 6. Why Front-endPerformance matters
  • 7. According to Yahoo:“80% of end-user response time isspent on the front-end”According to Steve Souders (Google performance guru):“80-90% of end-user responsetime is spent on the front-end”
  • 8. Ads CDN’s Services Syndicated ContentIntegration is happening on the client-side
  • 9. OPTIMIZING FRONT END• Majority of end user response time spent on front end• Easier to optimize front end• Time spent optimizing here will have greatest impact
  • 10. OPTIMIZE PAGE LOAD
  • 11. PAGE LOAD TIME IS IMPORTANTPage load time is critical to the success of a web site/app Google: +500 ms → -20% traffic Yahoo: +400 ms → -5-9% full-page traffic Amazon: +100 ms → -1% salesSmall performance flucutations affect traffic and sales!!!
  • 12. BEST PRACTICES• Reduce HTTP Requests • reduce overhead of page load • combine javascript and css into less number of files • combine images into sprites• Use a Content Delivery Network (CDN) • static content delivered by fast distributed network with low latency • content delivered closer to “last mile”
  • 13. BEST PRACTICES• Make Pages Cacheable • add expires header to pages • use on all static content • reduces HTTP requests• Use GZIP Page Compression • all modern browsers support GZIP compression • 60-80% savings on text-based content • No code changes required!
  • 14. BEST PRACTICES• Place Stylesheets at the Top • browser needs style info first to avoid repaints/reflows later CSS • keep stylesheets external • use <link>, do not use @import• Place Scripts at the Bottom • allow page content to be rendered first • keep scripts external to allow caching JavaScript
  • 15. BEST PRACTICES• Minify JavaScript and CSS • save bandwidth / download time • lots of tools to automate this for you• Post/pre Load Components • consider how you are loading content and scripts
  • 16. BEST PRACTICES• Maximize Paralell Downloads• Split components across domains• each browser limits paralell downloads per domain• enables browser to load more stuff in parallel• Optimize Images • avoid high-res images unless it is intentional • don’t let the browser scale your images • combine into sprites
  • 17. CSS SPRITES• One image contains multiple web images• CSS styles used to display correct web image, i.e. position, background-position
  • 18. RESPONSIVE INTERFACES
  • 19. A SINGLE BROWSER THREAD
  • 20. SINGLE THREAD IMPLICATIONS• Single UI Thread for both UI updates and JavaScript execution • only one of these can happen at a time! • Reason: JavaScript may cause UI updates... Page downloading and rendering must stop and wait for scripts to be downloaded and executed
  • 21. “0.1 second is about the limit for having the user feel that a system is reacting instantaneoulsy” - Jakob Nielsen, Usability ExpertTranslation: No single JavaScript should execute formore than 100 mS to ensure a responsive UI.
  • 22. No limit to how long this can run... function processData(items, processor, callback) { for (var i=0, len=items.length; i<len; i++) { processor(items[i]); } callback(); }Will run no more than 50 mS... funcion timedProcessData(items, processor, callback) { var todo = items.concat(); // clone items setTimeout(funcion() { var start = new Date(); do { processor(todo.shift()); } while (todo.length > 0 && (new Date() - start < 50)); if (todo.length > 0) { setTimeout(arguments.callee, 25); } else { callback(items); } }, 25); }
  • 23. WEB WORKERS• Commonly associated with HTML5• Allow for asynchronous JavaScript execution• JS runs in a seperate thread isolated from the DOM• Does not delay UI updates• Data can be passed to/from Web Workers
  • 24. Calling a Web Worker var worker = new Worker("worker.js"); // Watch for messages from the worker worker.onmessage = function(e){ // The message from the client: e.data }; worker.postMessage("start");The Web Worker client (worker.js) onmessage = function(e){ if ( e.data === "start" ) { // Do some computation done() } }; function done(){ // Send back the results to the parent page postMessage("done"); }
  • 25. LOADING & EXECUTING JAVASCRIPT
  • 26. WHY JAVASCRIPT?• Poorly written JavaScript is the most common reason for slow client-side performance • Loading • Parsing • Execution
  • 27. TYPICAL JAVASCRIPT PLACEMENT<html> <head> <link href=”style.css” rel=”stylesheet” type=”text/css”/> <script src=”myscript.js” type=”text/javascript”></script> <script src=”myscript.js” type=”text/javascript”></script> <script> function hello_world() { alert(‘hello world’); } var complex_data = // some complex calculation // </script> </head> <body> ... </body></html>
  • 28. BETTER JAVASCRIPT PLACEMENT<html> <head> <link href=”style.css” rel=”stylesheet” type=”text/css”/> </head> <body> ... <script src=”myscript.js” type=”text/javascript”></script> <script src=”myscript.js” type=”text/javascript”></script> <script> function hello_world() { alert(‘hello world’); } var complex_data = // some complex calculation </script> </body></html>
  • 29. COMBINE JAVASCRIPT FILES• Each script request requires HTTP performance overhead• Minimize overhead by combining scripts file.js file1.js file2.js file3.js => Browser Browser
  • 30. MINIFY JAVASCRIPT• Removes all unecessary space/comments from your JS files• Replace variables with short names• Easy to do at built-time with a tool• Checkout YUI Compressor, Closure Compiler... Avoid manual code-size optimization!
  • 31. NON-BLOCKING LOADS• AddJavaScript to a page in a way that does not block the browser thread ‣ Dynamic Script Elements ‣ Script Injection
  • 32. DYNAMIC SCRIPT ELEMENTS• JavaScript is downloaded and executed without blocking other page processes. var script = document.createElement(‘script’); script.type = “text/javascript”; script.src = “file1.js”; document.getElementsByTagName(“head”)[0].appendChild(script);
  • 33. SCRIPT INJECTION• Use Ajax to get script• Can control when script is parsed/executed• JavaScript must be served from same domain var xhr = XMLHttpRequest(); xhr.open(“get”, “file.js”, true); xhr.onreadystatechange = function() { if (xhr.readyState == 4) { if (xhr.status >= 200 && xhr.status < 300 || xhr.status == 304) { var script = document.createElement(“script”); script.type = “text/javascript”; script.text = xhr.responseText; document.body.appendChild(script); } } }; xhr.send(null);
  • 34. RECOMMENDED NONBLOCKING LOAD• Include the code necessary to dynamically load the the rest of the JS required for page init <script type="text/javascript" src="loader.js"></script> <script type="text/javascript"> loadScript("the-rest.js", function(){ Application.init(); }); </script> Optionally include the loadScript function directly in the page
  • 35. REAL WORLD USE• This technique is used by many JavaScript libraries including YUI and Dojo. <script type="text/javascript" src="http://yui.yahooapis.com/combo?3.0.0/build/yui/yui-min.js"></script> YUI().use("dom", function(Y){ Y.DOM.addClass(document.body, "loaded"); }); Dynamically loads the DOM utility and calls ‘loaded’ function when loading is complete.
  • 36. OPEN SOURCE JS LOADERSLots of libraries available to help with the JS load problem: • ControlJS • LabJS • RequireJS
  • 37. CONTROLJS• Progessive Enhancement is core to ControlJS philosophy• downloads scripts asynchronously• delays script execution until aftr the page has rendered• allows scripts to be downloaded and not executed
  • 38. CONTROLJS Async JS Loading var cjsscript = document.createElement(script); cjsscript.src = "control.js"; var cjssib = document.getElementsByTagName(script)[0]; cjssib.parentNode.insertBefore(cjsscript, cjssib);Replace these script includes:<script type="text/javascript" src="main.js"></script>with:<script type="text/cjs" data-cjssrc="main.js"></script>
  • 39. CONTROLJS Delayed Execution<script data-cjsexec=false type="text/cjs" data-cjssrc="jquery.min.js"></script><script data-cjsexec=false type="text/cjs" data-cjssrc="fg.menu.js"></script> Execute at a later time... examplesbtn.onclick = function() { CJS.execScript("jquery.min.js"); CJS.execScript("fg.menu.js", createExamplesMenu); };
  • 40. LABJS Async JS Loading<script src="LAB.js"></script>Load these scripts asynchronously:$LAB.script(mootools-1.3.js);$LAB.script(mootools-1.3.js).wait() .script(mootools-dependent-script.js);
  • 41. SUMMARY• Browser UI and JS share a single thread• Code execution blocks other browser processes such as UI painting• Put script tags at the bottom of page• Load as much JS dynamically as possible• Minimize and compress your JS
  • 42. DATA ACCESS
  • 43. ACCESSING DATAHow you store and access data can have a significantimpact on performance... JavaScript Scope Chain
  • 44. SCOPE CHAINBad (deeper scope chain referencing repeatedly)function innerHTMLLoop() { document.getElementById(ctrl1).innerHTML += a; document.getElementById(ctrl1).innerHTML += b; document.getElementById(ctrl1).innerHTML += c;}Better (save globals to local variables)function innerHTMLLoop2() { var el = document.getElementById(ctrl1); el.innerHTML += a; el.innerHTML += b; el.innerHTML += ‘c’;}
  • 45. DOM SCRIPTING
  • 46. DOCUMENT OBJECT MODEL • Document Object Model (DOM) is a language independent API for working with HTML and XML • DOM Scripting is expensive and a common cause of performance problems
  • 47. DOM/JS ISOLATION• DOM and JavaScript implementations are independent of each other in all major browsers• This causes overhead performance costs as these two pieces of code must interface JavaScri DOM pt Minimize how many times you cross this bridge
  • 48. BAD DOM SCRIPTINGBad (we cross the bridge 1500 times!)function innerHTMLLoop() { for (var count = 0; count < 1500; count++) { document.getElementById(here).innerHTML += a; }}Good (we cross the bridge 1 time)function innerHTMLLoop2() { var content = ; for (var count = 0; count < 1500; count++) { content += a; } document.getElementById(here).innerHTML += content;}
  • 49. REPAINTS AND REFLOWS A reflow occurs whenever you change the geometry of an element that is displayed on the page. A repaint occurs whenever you change the content of an element that is displayed on the screen.These are both expensive operations in terms of performance!
  • 50. AVOIDING REPAINTS/REFLOWS This will potentially cause 3 repaints/reflows... var el = document.getElementById(mydiv); el.style.borderLeft = 1px; el.style.borderRight = 2px; el.style.padding = 5px; Better... 1 repaint/reflow var el = document.getElementById(mydiv); el.style.cssText = border-left: 1px; border-right: 2px; padding: 5px;; or... var el = document.getElementById(mydiv); el.className = active;
  • 51. TOOLS
  • 52. TOOLS ARE YOUR FRIENDThe right tools can help a developer identify and fixperformance problems related to client-side behaviour. Profiling Timing functions and operations during script execution Network Analysis Examine loading of images, stylesheets, and scripts and their effect on page load and rendering
  • 53. FIREBUG•Firefox plugin•Debug JavaScript•View page load waterfall:
  • 54. PAGE SPEED•Extension to Firebug from Google•Provides tips for improving page performance
  • 55. Y-SLOW•Extension to Firebug from Yahoo•tips for improving page performance
  • 56. DYNATRACE AJAX EDITION•extension for IE, coming soon for Firefox•deeper client-side tracing than the firebug extensions
  • 57. SPEED TRACER•performance extension for Google Chrome•similar features to Dynatrace Ajax
  • 58. YUI PROFILER•profile JavaScript performance•developer must insert JS code
  • 59. MORE TOOLS...Internet Explorer Developer ToolsSafari Web InspectorChrome Developer ToolsLots of developer tools to debug performance!
  • 60. PERFOMANCE MONITORING
  • 61. SHOWSLOW collects: YSlow PageSpeed DyantraceIntegrate withWebPageTestto run tests. http://www.showslow.com/
  • 62. WEB PAGE TESTTests againstdedicated nodes.Agent deployedon test nodes.Image capture http://www.webpagetest.org/
  • 63. BOOMERANG <html> <head>JavaScript library for Real <script src="boomerang.js" type="text/javascript"></script> <script type="text/javascript"> BOOMR.init({User Monitoring (RUM) beacon_url: "http://yoursite.com/path/to/beacon.php" }); BOOMR.plugins.RT.startTimer("t_head"); </script>Released by Yahoo in <title>page title</title> <meta http-equiv="Content-type" content="text/html; charset=utf-8">2010 <link rel="stylesheet" type="text/css" href="../boomerang-docs.css"> <script type="text/javascript"> BOOMR.plugins.RT.endTimer("t_head").startTimer("t_body"); </script> </head>Beacon metrics to a <body> page body herecentral server <script type="text/javascript"> BOOMR.plugins.RT.endTimer("t_body"); </script> </body> </html> https://github.com/yahoo/boomerang
  • 64. W3C WEB PERFORMANCENew W3C Working Group focused on web performance.First recommendations: Navigation Timing - how fast does the page load Resource Timing - how fast do page resources load User Timing - user defined custom timing events http://www.w3.org/2010/webperf/
  • 65. DON’T WANT TO DOALL OF THIS YOURSELF???
  • 66. End-to-end application performance monitoring
  • 67. RESOURCES• Yahoo Exceptional Performance http://developer.yahoo.com/performance/• Google Web Performance http://code.google.com/speed• JavaScript: The Good Parts by Douglas Crockford• High Performance JavaScript by Nicholas Zakas• Even Faster Websites by Steve Souders• Steve Souders Site http://www.stevesouders.com• John Resig’s Blog http://www.ejohn.org
  • 68. QUESTIONS