How to read offline data from firestore in ionic3?

Hello to all,
I have create a app in ionic3 with cloud firestore it is working properly but in such a case if network is not available all the data is blank due to connection execeted requirement is that is if network is not available my initially loaded data is stored in the cache means user have to show initially loaded data instead of blank data.i have read the doc of the firestore but i don’ t understand how to implemented in our ionic3 tell my anyone how to implemented this functionality in ionic3?