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How to Follow Farcaster Users Owning a Specific NFT

This guide demonstrates how to follow Farcaster users who own a specific NFT. Check out this Getting started guide to learn how to set up your environment and get an API key. Before all that, initialize Neynar client:
Javascript
// npm i @neynar/nodejs-sdk
import { NeynarAPIClient, Configuration } from "@neynar/nodejs-sdk";

// make sure to set your NEYNAR_API_KEY .env
// don't have an API key yet? get one at neynar.com
const config = new Configuration({
  apiKey:process.env.NEYNAR_API_KEY,
});

const client = new NeynarAPIClient(config);
const signer = process.env.NEYNAR_SIGNER;
First, we need to get the addresses owning Milady. We can use the Alchemy NFT API to get the addresses of users who own the NFT.
Javascript
const getAddr = async (nftAddr: string): Promise<string[]> => {
  const apiKey = process.env.ALCHEMY_API_KEY;
  const baseUrl = `https://eth-mainnet.g.alchemy.com/nft/v3/${apiKey}/getOwnersForContract?`;
  const url = `${baseUrl}contractAddress=${nftAddr}&withTokenBalances=false`;

  const result = await fetch(url, {
    headers: { accept: "application/json" },
  });
  const data = await result.json();
  return data.owners;
};

// milady maker contract address
const nftAddr = "0x5af0d9827e0c53e4799bb226655a1de152a425a5";
const addrs = await getAddr(nftAddr);
Next, get Farcaster FIDs of each address, then filter out any undefined values.
Javascript
const fidLookup = async (addrs: string[]) => {
  const fids = await Promise.all(
    addrs.map(async (addr) => {
      try {
        const response = await client.fetchBulkUsersByEthOrSolAddress({addresses:addr});
        return response ? response.result.user.fid : undefined;
      } catch (error) {
        return undefined;
      }
    })
  );
  return fids.filter((fid) => fid !== undefined);
};

const fids = await fidLookup(addrs);
Then, we can use the Follow user endpoint to follow each user.
Javascript
const result = await client.followUser({ signerUuid:signer, targetFids:fids});
console.log(result);
Example output: 
{
  "success": true,
  "details": [
    {
      "success": true,
      "target_fid": 132
    },
    {
      "success": true,
      "target_fid": 78
    },
    {
      "success": true,
      "target_fid": 4262
    },
    {
      "success": true,
      "target_fid": 3602
    },
  ]
}
That’s it! You can now follow users who own a specific NFT easily with the Neynar SDK.

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