Subscribe to ERC20 Transfer events

subscribe-erc20-transfers.mjs

import { Contract, getDefaultProvider, utils } from "ethers";

const provider = getDefaultProvider("homestead");

const abi = [
    "function symbol() view returns (string)",
    "function decimals() view returns (uint8)",
    "event Transfer(address indexed from, address indexed to, uint value)",
];

const topicFilter = utils.id("Transfer(address,address,uint256)");

async function handler(log) {
    const hash = log.transactionHash;
    const contract = new Contract(log.address, abi, provider);

    let logDescription, symbol, decimals;
    try {
        logDescription = contract.interface.parseLog(log);
        symbol = await contract.symbol();
        decimals = await contract.decimals();
    } catch (err) {
        return;
    }

    const [from, to, value] = logDescription.args;
    const amount = `${utils.formatUnits(value, decimals)} ${symbol}`;

    console.log(`New Transfer ${hash}\n\tfrom: ${from}\n\tto: ${to}\n\tamount: ${amount}`);
}

provider.on({ topics: [topicFilter] }, handler);

subscribe-erc20-transfers.ts

import { Contract, getDefaultProvider, utils } from "ethers";
import { Log } from "@ethersproject/abstract-provider";
import { LogDescription } from "@ethersproject/abi";

const provider = getDefaultProvider("homestead");

const abi = [
    "function symbol() view returns (string)",
    "function decimals() view returns (uint8)",
    "event Transfer(address indexed from, address indexed to, uint value)",
];

const topicFilter = utils.id("Transfer(address,address,uint256)");

async function handler(log: Log) {
    const hash = log.transactionHash;
    const contract = new Contract(log.address, abi, provider);

    let logDescription: LogDescription, symbol: string, decimals: number;
    try {
        logDescription = contract.interface.parseLog(log);
        symbol = await contract.symbol();
        decimals = await contract.decimals();
    } catch (err) {
        return;
    }

    const [from, to, value] = logDescription.args as any;
    const amount = utils.formatUnits(value, decimals);

    console.log(
        `New Transfer ${hash}\n\tfrom: ${from}\n\tto: ${to}\n\tamount: ${amount} ${symbol}`
    );
}

provider.on(
    {
        topics: [topicFilter],
    },
    handler
);