Loads of my blog readers wanted to know..here is the perfect link to it.
For Dynamics CRM version 8.2 or below, do this:
var apiVersion = Xrm.Page.context.getVersion();
For Dynamics CRM version 9 or above, do this:
var apiVersion = Xrm.Utility.getGlobalContext().getVersion();
It will give you an expended version which includes minor and major versions. Now, all you have to is crop the number to get only initial number such as 9.1 in this case:
var shortVersion= apiVersion.substring(3, myStr.indexOf(“.”) -1);
then finally use it in your request as:
Hope this helps!