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JavaScript Performance

JavaScript Performance. stevesouders.com/docs/sfjs-20120112.pptx. Disclaimer: This content does not necessarily reflect the opinions of my employer. YSlow. Cuzillion. SpriteMe. Hammerhead. Web Performance Optimization. WPO. drives traffic improves UX increases revenue reduces costs.

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JavaScript Performance

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  1. JavaScript Performance stevesouders.com/docs/sfjs-20120112.pptx Disclaimer: This content does not necessarily reflect the opinions of my employer.

  2. YSlow Cuzillion SpriteMe Hammerhead

  3. Web Performance Optimization WPO • drives traffic • improves UX • increases revenue • reduces costs

  4. What’s the #1 cause of slow web pages?

  5. JAVASCRIPT!

  6. 31% { all requests containing “.js” are skipped

  7. http://httparchive.org/trends.php?s=intersection

  8. 1995: scripts in HEAD • <head> • <script src=‘a.js’></script> • </head> blocks other downloads (IE 6-7, images in IE, iframes) downloaded sequentially (IE 6-7) blocks rendering during download & parse-execute

  9. 2007: move scripts to bottom • ... • <script src=‘a.js’></script> • </body> doesn’t block other downloads downloaded sequentially in IE 6-7 blocks rendering during download & parse-execute

  10. 2009: load scripts async var se = document.createElement(‘script’); se.src = ‘a.js’; document.getElementsByTagName(‘head’)[0].appendChild(se); doesn’t block other downloads downloaded in parallel (all browsers) blocks rendering during parse-execute

  11. 2010: async + on-demand exec var se = new Image(); // Object se.onload = registerScript; se.src = ‘a.js’; separate download from parse-execute doesn’t block other downloads downloaded in parallel (all browsers) doesn’t block rendering until demanded

  12. 20??: markup

  13. script async & defer parsing doesn’t wait for script: • async– executed when available • defer – executed when parsing finished when is it downloaded? missing: • defer download AND execution • async/defer download, execute on demand

  14. 20??: markup <script src=‘a.js’ [async|defer|noexecute] [deferdownload]> doesn’t block downloads downloaded in parallel doesn’t block rendering until demanded doesn’t contend for a connection easier

  15. ControlJSa JavaScript module for making scripts load faster http://controljs.org/ just change HTML inline & external scripts • <script type=‘text/cjs’ • data-cjssrc=‘main.js’> • </script> • <script type=‘text/cjs’> • var name = getName(); • </script>

  16. ControlJSa JavaScript module for making scripts load faster download without executing • <script type=‘text/cjs’ • data-cjssrc=‘main.js’ • data-cjsexec=false> • <script> Later if/when needed: • CJS.execScript(src);

  17. GMail Mobile <script type=‘text/javascript’> /* var ... */ </script> get script DOM element's text remove comments eval() when invoked awesome for prefetching JS that might (not) be needed http://goo.gl/l5ZLQ

  18. localStorage

  19. yuiblog.com/blog/2007/01/04/performance-research-part-2/

  20. blaze.io/mobile/understanding-mobile-cache-sizes/

  21. Home screen apps on iPhone are slower because resources are re-requested even though they should be read from cache.

  22. localStorage window.localStorage: • setItem() • getItem() • removeItem() • clear() also sessionStorage all popular browsers, 5MB max http://dev.w3.org/html5/webstorage/ http://diveintohtml5.org/storage.html

  23. localStorage as cache 1st doc: write JS & CSS blocks to localStorage • mres.-0yDUQJ03U8Hjija: <script>(function(){... set cookie with entries & version • MRES=-0yDUQJ03U8Hjija:-4EaJoFuDoX0iloI:... later docs: read JS & CSS from localStorage • document.write( localStorage.getItem(mres.-0yDUQJ03U8Hjija) ); http://stevesouders.com/blog/2011/03/28/storager-case-study-bing-google/

  24. Google Analytics Async Snippet code.google.com/apis/analytics/docs/tracking/asyncTracking.html varga = document.createElement(‘script’); ga.type= ‘text/javascript’; ga.async= true; ga.src = (‘https:’ == document.location.protocol ? ‘https://ssl’ : ‘http://www’)+‘.google-analytics.com/ga.js’; vars = document.getElementsByTagName(‘script’)[0]; s.parentNode.insertBefore(ga, s);

  25. avoid mixed content warning protocol relative URLs have problems set src last stevesouders.com/blog/2010/02/10/5a-missing-schema-double-download/ varga = document.createElement(‘script’); ga.type= ‘text/javascript’; ga.async= true; ga.src = (‘https:’ == document.location.protocol ? ‘https://ssl’ : ‘http://www’)+‘.google-analytics.com/ga.js’; vars = document.getElementsByTagName(‘script’)[0]; s.parentNode.insertBefore(ga, s);

  26. previously: getElementsByTagName(‘head’)[0].appendChild(ga) HEAD might not exist Android 1.5, iPhone 3.0, Opera 8.50, Safari 3.2 stevesouders.com/blog/2010/05/11/appendchild-vs-insertbefore/ stevesouders.com/blog/2010/05/12/autohead-my-first-browserscope-user-test/ varga = document.createElement(‘script’); ga.type= ‘text/javascript’; ga.async= true; ga.src = (‘https:’ == document.location.protocol ? ‘https://ssl’ : ‘http://www’)+‘.google-analytics.com/ga.js’; vars = document.getElementsByTagName(‘script’)[0]; s.parentNode.insertBefore(ga, s);

  27. some browsers preserve execution order Firefox 3.6, Opera, OmniWeb stevesouders.com/tests/jsorder.php varga = document.createElement(‘script’); ga.type= ‘text/javascript’; ga.async= true; ga.src = (‘https:’ == document.location.protocol ? ‘https://ssl’ : ‘http://www’)+‘.google-analytics.com/ga.js’; vars = document.getElementsByTagName(‘script’)[0]; s.parentNode.insertBefore(ga, s);

  28. stevesouders.com/tests/jsorder.php

  29. some browsers preserve execution order Firefox 3.6, Opera, OmniWeb async=true fixes this (except Opera) stevesouders.com/tests/jsorder.php varga = document.createElement(‘script’); ga.type= ‘text/javascript’; ga.async= true; ga.src = (‘https:’ == document.location.protocol ? ‘https://ssl’ : ‘http://www’)+‘.google-analytics.com/ga.js’; vars = document.getElementsByTagName(‘script’)[0]; s.parentNode.insertBefore(ga, s);

  30. A B C <html> <head> <link rel=stylesheet ...> <style>...</style> <script [...]></script> </head> <body> <div> <p> <ul> </body> </html> onload: D

  31. A script loads sooner beacon fires sooner blocks other async (Opera) may block rendering <html> <head> <link rel=stylesheet ...> <style>...</style> <script [...]></script> </head> <body> <div> <p> <ul> </body> </html> onload:

  32. B script loads later beacon fires later blocks fewer async (Opera) may block rendering <html> <head> <link rel=stylesheet ...> <style>...</style> <script [...]></script> </head> <body> <div> <p> <ul> </body> </html> onload:

  33. script loads last beacon fires late doesn’t block async doesn’t block rendering C <html> <head> <link rel=stylesheet ...> <style>...</style> <script [...]></script> </head> <body> <div> <p> <ul> </body> </html> onload:

  34. script loads after page beacon fires very late doesn’t block async doesn’t block rendering onload fires sooner <html> <head> <link rel=stylesheet ...> <style>...</style> <script [...]></script> </head> <body> <div> <p> <ul> </body> </html> onload: D

  35. more

  36. stevesouders.com/blog/2011/12/01/silk-ipad-galaxy-comparison/stevesouders.com/blog/2011/12/01/silk-ipad-galaxy-comparison/

  37. stevesouders.com/mobileperf/mobileperfbkm.php

  38. Top 100 Top 1000

  39. takeaways WPO WebPagetest.org Cuzillion.com Browserscope.org ControlJS.org localStorage GA snippet is good Loadtimer.org MobilePerf.org HTTPArchive.org Velocity stevesouders.com

  40. @souders http://stevesouders.com/docs/sfjs-20120112.pptx

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