View local HTML files using web browser on iPad

Since the files are always local to the app in iOS. You can't open a html with apps like Safari and Chrome to load associated assets (js/images/css).

However, You could use apps like Documents to upload the folder and open in app browser (uiwebview).

Should work if the URL to assets in the html are relative.

You can create Web Apps for offline viewing by adding them to the home screen. To do this the web page must be written using HTML5 Offline Application Cache. See the below link for further details.

https://developer.apple.com/library/safari/documentation/iPhone/Conceptual/SafariJSDatabaseGuide/OfflineApplicationCache/OfflineApplicationCache.html