Once you have the intent and custom url scheme for your app set up, this javascript code at the top of a receiving page has worked for me on both iOS and Android:
This has only been tested on the Android browser. I am not sure about Firefox or Opera. The key is even though the Android browser will not throw a nice exception for you on window.open(custom_url, '_blank'), it will fail and return null which you can test later.
Update: using store_loc = "https://play.google.com/store/apps/details?id=com.raditaz"; to link to Google Play on Android.