IE10 has some wonderful enhancements in the HTML5 compliance area but remains a bear to develop JavaScript HTML5 when running on the WP8 as there is no way to debug the app
FWIW: Windows Phone 8.1 finally supports remote debugging. See http://blogs.msdn.com/b/visualstudioalm/archive/2014/04/04/diagnosing-mobile-website-issues-on-windows-phone-8-1-with-visual-studio.aspx