Developing High Performance Web Apps
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The document provides an overview of developing high performance web applications, focusing on optimizing front-end performance. It discusses why front-end performance matters, and provides best practices for optimizing page load time, developing responsive interfaces, and efficiently loading and executing JavaScript. The document also covers DOM scripting techniques, tools for profiling and analyzing performance, and how the performance monitoring service Gomez can be extended to better measure client-side metrics.
![DYNAMIC SCRIPT ELEMENTS
• JavaScript
is downloaded and executed without blocking
other page processes.
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Developing High Performance Web Apps
- 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 tim.fisher@compuware.com www.timothyfisher.com
- 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
- 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
- 16. A SINGLE BROWSER THREAD
- 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.
- 19. LOADING & EXECUTING JAVASCRIPT
- 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(); 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);
- 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="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.
- 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
- 31. DOM SCRIPTING
- 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'); 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';
- 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!
- 46. GOMEZ AND FRONT-END 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
- 48. ACTIVE ACTUAL
- 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 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
- 53. QUESTIONS