ReadonlylowerReturns lower bound, or undefined if none.
ReadonlylowerReturns true if the lower open flag is set, and false otherwise.
ReadonlyupperReturns upper bound, or undefined if none.
ReadonlyupperReturns true if the upper open flag is set, and false otherwise.
A key range can be a single value or a range with upper and lower bounds or endpoints. If the key range has both upper and lower bounds, then it is bounded; if it has no bounds, it is unbounded. A bounded key range can either be open (the endpoints are excluded) or closed (the endpoints are included). To retrieve all keys within a certain range, you can use the following code constructs:
MDN Reference