Issue: After upgrading to CRM 2015, you will notice that any javascript methods using getServerUrl will stop working. I was in the same boat and after debugging for a while, I found out that this method is not supported anymore in CRM 2015. In order to make this javascript work you will have to use getClientUrl instead.
Resolution: Replace getServerUrl with getClientUrl in all javascript methods/functions.
Power Platform Pulse 
Hi
Thanks for this information, does getClientUrl work in CRM 2013? I was thinking of changing the script before the upgrade.
Thanks
We are upgrading from 2011 to 2015. I tested the change in our 2011 test environment and it worked just fine. I see no reason why it would not work in 2013.