The getAllKeys() method of the IDBObjectStore interface returns an IDBRequest object retrieves record keys for all objects in the object store matching the specified parameter or all objects in the store if no parameters are given. 
  If a value is successfully found, then a structured clone of it is created and set as the result of the request object. 
 This method produces the same result for:
  - a record that doesn't exist in the database
  - a record that has an undefined value
  
  To tell these situations apart, you need to call the openCursor() method with the same key. That method provides a cursor if the record exists, and no cursor if it does not. 
 
getAllKeys()
getAllKeys(query)
getAllKeys(query, count)
  
An IDBRequest object on which subsequent events related to this operation are fired.
 If the operation is successful, the value of the request's result property is an Array of the keys for all records matching the given query, up to the value of count, if count was supplied.
 
This method may raise a DOMException of one of the following types:
  - 
TransactionInactiveError DOMException
  -  
Thrown if this IDBObjectStore's transaction is inactive.
   - 
DataError DOMException
  -  
Thrown if the key or key range provided contains an invalid key or is null.
   - 
InvalidStateError DOMException
  -  
Thrown if the IDBObjectStore has been deleted or removed.