Last week at Velocity we hosted a Birds of a Feather Session (BoF) and offered the attendees to analyze their web sites using dynaTrace Ajax Edition. Besides finding the typical performance problems (no cache settings, too many images, not minimized content, …) we found several sites that had one interesting problem in common: OLD VERSIONS of JavaScript libraries such as YUI, jQuery or SPRY.
Why are outdated JavaScript Libraries a problem?

JavaScript libraries such as jQuery provide functions that make it easy for web developers to achieve certain things, e.g.: change the style of certain DOM elements. Most of these libraries therefore provide methods called $, $$ or find that allow finding DOM elements by ID, Tag Name, CSS Class Name or specific DOM attribute values.

The following is a screenshot of the Performance Report analyzing the Boston Bruins Page on msn.foxsports.com using Firefox 3.6. The Performance Report highlights 3 interesting things:

  • High Client Time (3.5 seconds in JavaScript execution until the Page was Fully Loaded)
  • 39 JavaScript! blocks that executed longer than 20ms
  • 38 calls to Spry.$$ for looking up an element by Class Name with an average of 80ms execution time

Continue reading the full blog by Andreas Grabner


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