What's the best way to fetch FA2 (NFT) owners?

[Dreitser]

Hi.
We're a bit stuck trying to find out if a wallet is an owner of a certain FA2 (NFT) using Taquito. Can anyone point us in the right direction?

[claudebarde]

In general, FA2 contracts have a bigmap (sometimes called ledger or balances) whose keys are the users’ addresses together with a token id if that’s relevant to the use case.
You can get the storage of the contract with await contract.storage() and check if the user’s address is a key of the bigmap, for example, await storage.ledger.get(USER_ADDRESS). If there is no matching key, the promise returns undefined, otherwise, it returns the associated value.