BNB Smart Chain - Web3js Listen to Events

web3master

Example of how to listen to all BEP20 token smart contract transfer events in real time with Web3Js and WebSockets.

const Web3 = require('web3');
const web3 = new Web3('wss://rpc-bsc.bnb48.club');

let options = {
    topics: [
        web3.utils.sha3('Transfer(address,address,uint256)')
    ]
};

const abi = [
    {
        "constant": true,
        "inputs": [],
        "name": "symbol",
        "outputs": [
            {
                "name": "",
                "type": "string"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    },
    {
        "constant": true,
        "inputs": [],
        "name": "decimals",
        "outputs": [
            {
                "name": "",
                "type": "uint8"
            }
        ],
        "payable": false,
        "stateMutability": "view",
        "type": "function"
    }
];

let subscription = web3.eth.subscribe('logs', options);

async function collectData(contract) {
    const [decimals, symbol] = await Promise.all([
        contract.methods.decimals().call(),
        contract.methods.symbol().call()
    ]);
    return { decimals, symbol };
}

subscription.on('data', event => {
    if (event.topics.length == 3) {
        let transaction = web3.eth.abi.decodeLog([{
            type: 'address',
            name: 'from',
            indexed: true
        }, {
            type: 'address',
            name: 'to',
            indexed: true
        }, {
            type: 'uint256',
            name: 'value',
            indexed: false
        }],
            event.data,
            [event.topics[1], event.topics[2], event.topics[3]]);

        const contract = new web3.eth.Contract(abi, event.address)

        collectData(contract).then(contractData => {
            const unit = Object.keys(web3.utils.unitMap).find(key => web3.utils.unitMap[key] === web3.utils.toBN(10).pow(web3.utils.toBN(contractData.decimals)).toString());

            console.log(`Transfer of ${web3.utils.fromWei(transaction.value, unit)} ${contractData.symbol} from ${transaction.from} to ${transaction.to}`)
        
            if (event.address == '0x55d398326f99059fF775485246999027B3197955') { console.log('Specified ERC-20 transfer!') };

        })
    }
});

subscription.on('error', err => { throw err });
subscription.on('connected', nr => console.log('Subscription on ERC-20 started with ID %s', nr));