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This guide refers to this API

Farcaster users can connect their FID (Farcaster ID) with an Ethereum or Solana address. This guide demonstrates how to get information about a user given their address. Check out this Getting started guide to learn how to set up your environment and get an API key. First, initialize the client: 
// 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);
To get vitalik.eth’s Farcaster profile: 
// vitalik.eth
const addr = "0xd8da6bf26964af9d7eed9e03e53415d37aa96045";
const user = await client.fetchBulkUsersByEthOrSolAddress({addresses: [addr]});

console.log(user);
Example output: 
{
  result: {
    user: {
      fid: 5650,
      custodyAddress: "0xadd746be46ff36f10c81d6e3ba282537f4c68077",
      username: "vitalik.eth",
      displayName: "Vitalik Buterin",
      pfp: [Object ...],
      profile: [Object ...],
      followerCount: 14769,
      followingCount: 70,
      verifications: [ "0xd8da6bf26964af9d7eed9e03e53415d37aa96045" ],
      activeStatus: "active"
    }
  }
}
For addresses with multiple verifications, it will all resolve to the same user: 
// dwr.eth
const addr1 = "0xd7029bdea1c17493893aafe29aad69ef892b8ff2";
const addr2 = "0xa14b4c95b5247199d74c5578531b4887ca5e4909";

// use Promise.all to make multiple requests in parallel
const users = await Promise.all([
  client.fetchBulkUsersByEthOrSolAddress({addresses: [addr1]}),
  client.fetchBulkUsersByEthOrSolAddress({addresses: [addr2]}),
]);

console.log(users[0] === users[1]); // true
console.log(users[0]);
They both resolve to: 
{
  result: {
    user: {
      fid: 3,
      custodyAddress: "0x6b0bda3f2ffed5efc83fa8c024acff1dd45793f1",
      username: "dwr.eth",
      displayName: "Dan Romero",
      pfp: [Object ...],
      profile: [Object ...],
      followerCount: 19326,
      followingCount: 2702,
      verifications: [ "0xd7029bdea1c17493893aafe29aad69ef892b8ff2", "0xa14b4c95b5247199d74c5578531b4887ca5e4909",
        "0xb877f7bb52d28f06e60f557c00a56225124b357f", "0x8fc5d6afe572fefc4ec153587b63ce543f6fa2ea"
      ],
      activeStatus: "active"
    }
  }
}

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