How to find all the NFTs, ERC721 and ERC1155, owned by address of *a certain collection*?

Question

How to find all the NFTs of a certain collection, ERC721 and ERC1155, owned by address ? In ethers.js

update #1

Let's say, I'm an owner of an NFT collection who sells them via my website.

When user comes to my website and logs in with his wallet, won't I be able to find out what NFTs of my collection he's a holder of?

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I could upgrade an NFT smart contract if needed.

Answer 1

This requires indexing the blockchain. This is fairly simple using Moralis APIs. https://docs.moralis.io/web3-data-api/evm/how-to-get-nft-owners-by-an-address

Alternative, you can do this using ethers.js:

const { ethers } = require('ethers');

const networkUrl = 'https://eth-mainnet.your-moralis-server.com/APIKEY';
const provider = new ethers.providers.JsonRpcProvider(networkUrl);
const contractAddress = '0x...'; // Replace with the actual contract address
const abi = [...]; // Replace with the ABI of the ERC721 or ERC1155 contract

const contract = new ethers.Contract(contractAddress, abi, provider);

For ERC721: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/ffceb3cd988874369806139ae9e59d2e2a93daec/contracts/token/ERC721/ERC721.sol#L60

const ownerAddress = '0x...'; // Replace with the owner's address

const balance = await contract.balanceOf(ownerAddress);

For ERC1155: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/ffceb3cd988874369806139ae9e59d2e2a93daec/contracts/token/ERC1155/ERC1155.sol#L78

const ownerAddress = '0x...'; // Replace with the owner's address
const tokenIds = [1, 2, 3]; // Replace with the desired token IDs

const balances = await contract.balanceOfBatch([ownerAddress], tokenIds);

The balance or balances variable will contain the number of NFTs owned by the address. You can then loop through the token IDs.

Answer 2

Use a Node as a service that provides additional NFT endpoints. I like to use alchemy. It provides the getNFTsForOwner endpoint that does the job.