How do I preload url's in ionic?

I am pretty new to ionic 1 and I am working on an application (with ionic 1 and angularjs) with multiple url’s where each url brings up a list of categories, followed by a list of items for each categories and each item has a documenturl. How do i preload all these url’s on launch in the background but not display them.Is there any way this can be achieved? a good code sample or tutorial will help greatly. Also, please let me know if this will be the best approach, as in pre loading and pre caching all content upon launch or should it be done category by category or some other way.

Thanks in advance!