Hi,
I would say to use XRMToolBox for CRM 2013 for making your odata queries quickly.
The link is Toolbox for Dynamics CRM 2011/2013
Once you have your odata query ready, you can follow this post for utilizing the odata query in your JavaScript file.
The link is
oData Call in JavaScript
You will be able to retrieve the data similarly as you were retrieving in CRM 2011.
Moreover if you can also have a look on this link which is related to
fetchXml exception in CRM 2013 which is an advantage over fetchXml in CRM 2011. (might be useful somewhere in other scenarios.)
I hope this helps to resolve your issue.
Thanks & Regards,
Anubhav Bajpai