I want to get the sObject name in JS section of VF Page . I have the object id .
var objectID = ; objectID = Id;
Something akin to :
String sObjName = myId.getSObjectType().getDescribe().getName();
I understood you want to get this information with JS only. Then you'd have to use a Salesforce API or code the mapping for yourself.
If you can also use Apex, a Controller or Controller Extension will do the trick.