jQuery Grid Plugin - jqGrid

I am going to use JqGrid for many different web pages. And I have some custom formatter, and custom edittype for example, I want to use datepicker to edit dates

so, instead of using colModel's edittype as custom, and provide custom functions to do that, I would like "if possible" to write an extension to jqgrid edittype, so I can just write "date", and I will write an extension to replace it with the datepickeer. As I said, it is for re-usability, so instead of doing custom edit type for every web page/jqgrid, I could do it only once in that place. Is there any documentation on how to extend jqgrid?