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CS193H: High Performance Web Sites Lecture 15: Rule 12 – Remove Duplicate Scripts

CS193H: High Performance Web Sites Lecture 15: Rule 12 – Remove Duplicate Scripts. Steve Souders Google souders@cs.stanford.edu. Duplicate Scripts. hurts performance extra HTTP requests if not cacheable http://stevesouders.com/hpws/dupe-scripts.php IE and FF extra executions

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CS193H: High Performance Web Sites Lecture 15: Rule 12 – Remove Duplicate Scripts

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  1. CS193H:High Performance Web SitesLecture 15: Rule 12 – Remove Duplicate Scripts Steve Souders Google souders@cs.stanford.edu

  2. Duplicate Scripts hurts performance • extra HTTP requests if not cacheable http://stevesouders.com/hpws/dupe-scripts.php IE and FF • extra executions http://stevesouders.com/hpws/dupe-scripts-cached10.php all browsers atypical? • happens with ads http://www.aol.com/ adsonar.js (6K) loaded six times • happens with iframes http://www.ossamples.com/recipes/ fc-os-ext.js (15K), gadgets_en.js (155K) each loaded 3 times

  3. Script Insertion Functions <?php function insertScript($jsfile) { if ( alreadyInserted($jsfile) ) { return; } pushInserted($jsfile); if ( hasDependencies($jsfile) ) { $dependencies = getDependencies($jsfile); for ( $i = 0; $i < count($dependencies); $i++ ) { insertScript($dependencies[$i]); } } echo '<script type="text/javascript" src="' . getVersion($jsfile) . '"></script>"; } ?>

  4. Web 100 Profile project Aravind and I added 4 columns to compare double checks: • delta YSlow = YSlow1 – YSlow2 • delta %age time = ( (backend1/total1) – (backend2/total2) ) • delta # requests % = ( (requests1 – requests2)/requests1 ) • delta total size % = ( (size1 – size2)/size1 ) goals: <10 & <20% & <10% & <20% ~half of the sites had deltas bigger than this

  5. Homework 11/7 11:59pm – rules 4-10 applied to your "Improving a Top Site" class project 11/12 3:15pm – Web 100 Double Check • look at your rows in Web 100 spreadsheet • double-check your entries for any rows in red • update incorrect entries • enter "y" in "Double Checked" column

  6. Questions What are two typical causes of duplicate scripts? In what way(s) can duplicate scripts be bad for performance?

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