Got legacy code? You can’t sweep it under the rug anymore. It’s a blocker to upgrading. You will need the Custom Code tool created by the CRM team to root these issues out.

Learn more here http://blogs.msdn.com/b/crm/archive/2013/08/23/check-your-javascript-code-to-prepare-for-your-upgrade.aspx

Download the tool here http://www.microsoft.com/en-us/download/details.aspx?id=30151

Legacy Code won’t work in CRM 2015