JS vs Flex ArcGIS Server Sample Viewers

In recent weeks, ESRI has released 2 versions of a sample viewer application based on both their latest development platforms, the JS platform (released January 2009) and the Flex platform (released November 2008, updated February 2009). They both look and function similarly out of the box. Each features a icon oriented navigation bar based on various functional classes including maps, navigation, tools and resources. They both use REST based ArcGIS Server services both dynamically generated and cached very easily (although I was able to add ArcIMS Service Support to the Flex version without much hassle). Each features some pretty nice design patterns which allow developers to worry less about core functionality. Custom functions are implemented as "widgets" which function independently of the software core.

After tinkering with the Flex application for a few weeks and having a look at the JS version, I have a few impressions to share. First, they both use design patterns (Container Event Bus and Dependence Injection) that help decouple core functionality from custom functionality and really make it easy to extend. The flex viewer, based on Adobe's Opensource Flex 3.2 platform is very sexy and alleviates many cross-browser compatibility issues because of its required Flash plugin. Recently released as an opensource project, Flex offers a rich user experience with flashy graphical displays and fluid GUI performance. However, it requires an specific IDE based on the Eclipse IDE called Flex Builder which is rather pricey (ranging from $200.00 - $700.00). I have had the fortune of getting the IDE and have begun some "widget building" myself and have found it to be quite easy. I was able to construct a simple Map Navigation Widget in just a few days without any prior Flex development experience.While I haven't tinkered as much with the JS version, my initial impression is that it is also very slick and does not require a plugin. However, it's sex appeal is lacking a bit compared to the Flex version and it sounds as if (based on comments from the sample download blog) that it has some issues in IE 7.