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

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1 CS193H: High Performance Web Sites Lecture 15: Rule 12 – Remove Duplicate Scripts Steve Souders Google

2 announcements

3 Duplicate Scripts hurts performance extra HTTP requests if not cacheable IE and FF extra executions all browsers atypical? happens with ads adsonar.js (6K) loaded six times happens with iframes fc-os-ext.js (15K), gadgets_en.js (155K) each loaded 3 times

4 Script Insertion Functions "; } ?>

5 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

6 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

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


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