How to Delegate Token Accounts

You can set a delegate with an allowed amount. After you setting, the delegate is like an another owner of your token account.

A token account can only delegate to one account at a time.

import {
  clusterApiUrl,
  Connection,
  PublicKey,
  Keypair,
  Transaction,
  sendAndConfirmTransaction,
} from "@solana/web3.js";
import {
  approveChecked,
  createApproveCheckedInstruction,
} from "@solana/spl-token";
import bs58 from "bs58";

(async () => {
  // connection
  const connection = new Connection(clusterApiUrl("devnet"), "confirmed");

  // 5YNmS1R9nNSCDzb5a7mMJ1dwK9uHeAAF4CmPEwKgVWr8
  const feePayer = Keypair.fromSecretKey(
    bs58.decode(
      "588FU4PktJWfGfxtzpAAXywSNt74AvtroVzGfKkVN1LwRuvHwKGr851uH8czM5qm4iqLbs1kKoMKtMJG4ATR7Ld2",
    ),
  );

  // G2FAbFQPFa5qKXCetoFZQEvF9BVvCKbvUZvodpVidnoY
  const alice = Keypair.fromSecretKey(
    bs58.decode(
      "4NMwxzmYj2uvHuq8xoqhY8RXg63KSVJM1DXkpbmkUY7YQWuoyQgFnnzn6yo3CMnqZasnNPNuAT2TLwQsCaKkUddp",
    ),
  );

  const randomGuy = Keypair.generate();

  const mintPubkey = new PublicKey(
    "8mAKLjGGmjKTnmcXeyr3pr7iX13xXVjJJiL6RujDbSPV",
  );
  const tokenAccountPubkey = new PublicKey(
    "GMxZfDmpR1b3vdJYXHzdF5noVLQogZuUAsDHHQ3ytPfV",
  );

  // 1) use build-in function
  {
    let txhash = await approveChecked(
      connection, // connection
      feePayer, // fee payer
      mintPubkey, // mint
      tokenAccountPubkey, // token account
      randomGuy.publicKey, // delegate
      alice, // owner of token account
      1e8, // amount, if your deciamls is 8, 10^8 for 1 token
      8, // decimals
    );
    console.log(`txhash: ${txhash}`);
  }
  // or

  // 2) compose by yourself
  {
    let tx = new Transaction().add(
      createApproveCheckedInstruction(
        tokenAccountPubkey, // token account
        mintPubkey, // mint
        randomGuy.publicKey, // delegate
        alice.publicKey, // owner of token account
        1e8, // amount, if your deciamls is 8, 10^8 for 1 token
        8, // decimals
      ),
    );
    console.log(
      `txhash: ${await sendAndConfirmTransaction(connection, tx, [
        feePayer,
        alice /* fee payer + owner */,
      ])}`,
    );
  }
})();