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Developing High Performance Web Apps


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An overview of some ways developers can improve the performance of their web applications.

An overview of some ways developers can improve the performance of their web applications.

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  • 1. PERFOMANCE MATTERS DEVELOPING HIGH PERFORMANCE WEB APPS Timothy Fisher Compuware September 15, 2010
  • 2. WHO AM I? Timothy Fisher Technical Consultant (Eagle) Compuware @tfisher
  • 3. AGENDA • Why Front-end Performance Matters • Optimize Page Load • Responsive Interfaces • Loading and Executing JavaScript
  • 4. AGENDA • DOM Scripting • Tools • Gomez and Front-End Performance • Questions An overview to spark thought and further investigation
  • 5. Why Front-end Performance matters
  • 6. According to Yahoo: “80% of end-user response time is spent on the front-end” According to Steve Souders (Google performance guru): “80-90% of end-user response time is spent on the front-end”
  • 7. Ads CDN’s Services Syndicated Content Integration is happening on the client-side
  • 9. PAGE LOAD TIME IS IMPORTANT Page 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% sales Small performance flucutations affect traffic and sales!!!
  • 10. BEST PRACTICES • Minimize HTTP Requests • combine javascript and css into less number of files • consider sprites for combining images • Use a Content Delivery Network (CDN) • static content delivered by fast distributed network with low latency
  • 11. BEST PRACTICES • Make Pages Cacheable • use appropriate header tags • Use GZIP Page Compression • all modern browsers support GZIP compression
  • 12. BEST PRACTICES • Place Stylesheets at the Top • browser needs style info first to avoid repaints/reflows later • Place Scripts at the Bottom • allow page content to be rendered first
  • 13. 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
  • 14. BEST PRACTICES • Split Components Across Domains • 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
  • 17. SINGLE THREAD IMPLICATIONS • Single UI Thread for both UI updates and JavaScript execution • only one of these can happen at a time! Page downloading and rendering must stop and wait for scripts to be downloaded and executed
  • 18. “0.1 second is about the limit for having the user feel that a system is reacting instantaneoulsy” - Jakob Nielsen, Usability Expert Translation: No single JavaScript should execute for more than 100 mS to ensure a responsive UI.
  • 20. WHY JAVASCRIPT? • Poorly written JavaScript is the most common reason for slow client-side performance • Loading • Parsing • Execution
  • 21. 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>
  • 22. 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>
  • 23. 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
  • 24. 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!
  • 25. NON-BLOCKING LOADS • AddJavaScript to a page in a way that does not block the browser thread ‣ Dynamic Script Elements ‣ Script Injection
  • 26. 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);
  • 27. SCRIPT INJECTION • Use Ajax to get script • Can control when script is parsed/executed • JavaScript must be served from same domain var xhr = XMLHttpRequest();“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);
  • 28. RECOMMENDED NONBLOCKING LOAD • Includethe code necessary to dynamically 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
  • 29. REAL WORLD USE • This technique is used by many JavaScript libraries including YUI and Dojo. <script type="text/javascript" src=""></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.
  • 30. 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
  • 32. 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
  • 33. 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
  • 34. BAD DOM SCRIPTING Bad (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; }
  • 35. 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!
  • 36. AVOIDING REPAINTS/REFLOWS This will potentially cause 3 repaints/reflows... var el = document.getElementById('mydiv'); = '1px'; = '2px'; = '5px'; Better... 1 repaint/reflow var el = document.getElementById('mydiv'); = 'border-left: 1px; border-right: 2px; padding: 5px;'; or... var el = document.getElementById('mydiv'); el.className = 'active';
  • 37. TOOLS
  • 38. TOOLS ARE YOUR FRIEND The right tools can help a developer identify and fix performance 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
  • 39. FIREBUG •Firefox plugin •Debug JavaScript •View page load waterfall:
  • 40. PAGE SPEED •Extension to Firebug from Google •Provides tips for improving page performance
  • 41. Y-SLOW •Extension to Firebug from Yahoo •tips for improving page performance
  • 42. DYNATRACE AJAX EDITION •extension for IE, coming soon for Firefox •deeper client-side tracing than the firebug extensions
  • 43. SPEED TRACER •performance extension for Google Chrome •similar features to Dynatrace Ajax
  • 44. YUI PROFILER •profile JavaScript performance •developer must insert JS code
  • 45. MORE TOOLS... Internet Explorer Developer Tools Safari Web Inspector Chrome Developer Tools Lots of developer tools to debug performance!
  • 47. GOMEZ Gomez is the web performance division of Compuware •Active Monitoring synthetic tests using a dedicated node and a Gomez controlled browser •Actual Monitoring tests the actual end-user experience by transmitting data while users are browsing to a Gomez server
  • 49. GOMEZ ACTIVE • Synthetic tests • Uses nodes in Gomez network to perform web application testing. • Today pure client-side metrics are not collected
  • 50. GOMEZ ACTUAL • Real User Monitoring (RUM) • JavaScript ‘tags’ inserted into web pages. • Tags report performance metrics to Gomez server • Page and object load performance metrics
  • 51. EXTENDING ACTIVE/ACTUAL •Desire to collect more client-side metrics •JavaScript - load, parse, execution timing •CSS - load, parse timing •full Waterfall page load metrics •Attribute client-side performance to specific sources (i.e. javascript library from vendor abc is the source of your slow performance) •Expose full end-to-end performance
  • 52. RESOURCES • Yahoo Exceptional Performance • Google Web Performance • JavaScript: The Good Parts by Douglas Crockford • High Performance JavaScript by Nicholas Zakas • Even Faster Websites by Steve Souders • Steve Souders Site • John Resig’s Blog