1

What I'm trying to do:

I'm trying to listen to any event happening on a contract. Since I'm doing this for the first time, I chose a popular liquidity pool, the "Cake" liquidity pool on Binance Smart Chain. Here's the code (I'm using version 5.7.0 of ethers js):

const ethers = require("ethers");
var rpc_url = "https://bsc-dataseed.binance.org/";
let provider = new ethers.providers.JsonRpcProvider(rpc_url);

var contractAddress = "0x0ed7e52944161450477ee417de9cd3a859b14fd0";

// abi copied from https://bscscan.com/address/0x0ed7e52944161450477ee417de9cd3a859b14fd0#code
var CONTRACT_ABI = '[{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"sender","type":"address"},{"indexed":false,"internalType":"uint256","name":"amount0","type":"uint256"},{"indexed":false,"internalType":"uint256","name":"amount1","type":"uint256"},{"indexed":true,"internalType":"address","name":"to","type":"address"}],"name":"Burn","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"sender","type":"address"},{"indexed":false,"internalType":"uint256","name":"amount0","type":"uint256"},{"indexed":false,"internalType":"uint256","name":"amount1","type":"uint256"}],"name":"Mint","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"sender","type":"address"},{"indexed":false,"internalType":"uint256","name":"amount0In","type":"uint256"},{"indexed":false,"internalType":"uint256","name":"amount1In","type":"uint256"},{"indexed":false,"internalType":"uint256","name":"amount0Out","type":"uint256"},{"indexed":false,"internalType":"uint256","name":"amount1Out","type":"uint256"},{"indexed":true,"internalType":"address","name":"to","type":"address"}],"name":"Swap","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"uint112","name":"reserve0","type":"uint112"},{"indexed":false,"internalType":"uint112","name":"reserve1","type":"uint112"}],"name":"Sync","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"constant":true,"inputs":[],"name":"DOMAIN_SEPARATOR","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"MINIMUM_LIQUIDITY","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"PERMIT_TYPEHASH","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"","type":"address"},{"internalType":"address","name":"","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"to","type":"address"}],"name":"burn","outputs":[{"internalType":"uint256","name":"amount0","type":"uint256"},{"internalType":"uint256","name":"amount1","type":"uint256"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"decimals","outputs":[{"internalType":"uint8","name":"","type":"uint8"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"factory","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"getReserves","outputs":[{"internalType":"uint112","name":"_reserve0","type":"uint112"},{"internalType":"uint112","name":"_reserve1","type":"uint112"},{"internalType":"uint32","name":"_blockTimestampLast","type":"uint32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"_token0","type":"address"},{"internalType":"address","name":"_token1","type":"address"}],"name":"initialize","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"kLast","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"to","type":"address"}],"name":"mint","outputs":[{"internalType":"uint256","name":"liquidity","type":"uint256"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"internalType":"address","name":"","type":"address"}],"name":"nonces","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"},{"internalType":"uint256","name":"deadline","type":"uint256"},{"internalType":"uint8","name":"v","type":"uint8"},{"internalType":"bytes32","name":"r","type":"bytes32"},{"internalType":"bytes32","name":"s","type":"bytes32"}],"name":"permit","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"price0CumulativeLast","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"price1CumulativeLast","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"to","type":"address"}],"name":"skim","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"internalType":"uint256","name":"amount0Out","type":"uint256"},{"internalType":"uint256","name":"amount1Out","type":"uint256"},{"internalType":"address","name":"to","type":"address"},{"internalType":"bytes","name":"data","type":"bytes"}],"name":"swap","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"sync","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"token0","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"token1","outputs":[{"internalType":"address","name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"value","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"}]';

let contract = new ethers.Contract(contractAddress, CONTRACT_ABI, provider);

contract.on('*', event => {
  console.log(' ... something happened ...');
});

Result:

Nothing ends up happening. The code doesn't fail, it runs, but for some reason the code isn't listening to any event happening, even though I do in fact see events happening on that liquidity pool on dextools.

Question:

Does anyone know why this is happening? I believe I did everything properly to listen to an event on the Cake liquidity pool contract, however nothing seems to be happening.

1
  • I tested your code and it works with other RPCs, so try changing that. There's a list here for example chainlist.org/?search=bsc
    – 0xSanson
    May 2, 2023 at 11:14

1 Answer 1

1

Use a targeted listener like 'Transfer', 'Approval', etc.

Also, use a different RPC; Chainstack offers free elastic BSC RPCs that worked perfectly for me here.

After changing these two things, this code works fine.

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