Transferring tokens in a contract using ethers.js

gistfile1.txt

const ethers = require('ethers');

const { Contract, Wallet, providers } = ethers;

const CONTRACT_ADDRESS = '<contract-address-hash>';
const CONTRACT_ABI = '<contract-abi-json>';
const PRIVATE_KEY = '<private-key-hash>';
const DESTINATION_WALLET = '<destination-address-hash>';
const AMOUNT = '<tokens-amount>';

const PROVIDER = providers.getDefaultProvider();
const wallet = new Wallet(PRIVATE_KEY);

class CustomSigner {

    constructor(wallet) {
        this.wallet = wallet;
        this.provider = PROVIDER;
    }

    getAddress() {
        return Promise.resolve(this.wallet.getAddress());
    }

    sign(transaction) {
        return Promise.resolve(this.wallet.sign(transaction));
    }
}

const contract = new Contract(CONTRACT_ADDRESS, CONTRACT_ABI, new CustomSigner(wallet));

const walletAddress = wallet.getAddress();
console.log("Current wallet:", walletAddress);

contract.functions.balanceOf(walletAddress)
    .then(({ balance }) => console.log("Balance:", balance.toString()));

const gasLimit = 40000;
const gasPrice = 0xBEBC200; // 1 gwei
const options = { gasLimit, gasPrice };

const provider = PROVIDER;

provider.on(walletAddress, blockNumer => console.log("Balance changed in block", blockNumer));

contract.functions.transfer(DESTINATION_WALLET, AMOUNT, options)
    .then(txn => {
	    console.log("Waiting for confirmation on transaction", txn);
	    provider.waitForTransaction(txn).then(transaction => {
		    console.log("Transaction mined:", transaction);
	    });

	    provider.on(txn, txon => console.log("Mined transaction:", txon));
    });