• If you want to integrate Farcaster auth for your users, easiest way to start is Sign in with Neynar (Neynar pays all onchain fee)
  • If you want dedicated signers for your user or bot, simplest to clone this example app for quickstart
This guide demonstrates adding an Ethereum address verification with the Neynar SDK. 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);
const signer = process.env.NEYNAR_SIGNER;
Then like a cast: 
const hash = "0x6932a9256f34e18892d498abb6d00ccf9f1c50d6";
client.publishReaction({ signerUuid: signer, reactionType: "like", target:hash });
Recasting works the same way, just replace “like” with “recast”: 
const hash = "0x6932a9256f34e18892d498abb6d00ccf9f1c50d6";
client.publishReaction({ signerUuid: signer, reactionType: "like", target:hash });
The end result should look like this: 
{
  success: true;
}
To verify that the reaction was published, you can fetch the cast’s reactions: 
const types = ReactionsType.All;
const reactions = await client.fetchCastReactions({ hash, types: [types] });
console.log(reactions);
Which would print out 
{
  "result": {
    "casts": [
      {
        "type": "like",
        "hash": "0x691fabb3fc58bd4022d4358b2bc4f44469ad959a",
        "reactor": {
          "fid": "4640",
          "username": "picture",
          "displayName": "Picture",
          "pfp": {
            "url": "https://lh3.googleusercontent.com/erYudyT5dg9E_esk8I1kqB4bUJjWAmlNu4VRnv9iUuq_by7QjoDtZzj_mjPqel4NYQnvqYr1R54m9Oxp9moHQkierpY8KcYLxyIJ"
          },
          "followerCount": "45",
          "followingCount": "57"
        },
        "timestamp": "2023-12-10T15:26:45.000Z",
        "castHash": "0x6932a9256f34e18892d498abb6d00ccf9f1c50d6"
      }
    ],
    "next": {
      "cursor": null
    }
  }
}
That’s it! You can now like or recast any cast on Farcaster. PS - to learn more about how writes technically work on Farcaster, read Write to Farcaster with Neynar Managed Signers

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