How to get what token is swapped for decoded swap event?

Question

So I made program that listens for swap events and decode it and how would I get what is swapped eg usdt to ethereum or etherum to usdt, Here is output:

{
  name: 'Swap',
  events: [
    {
      name: 'sender',
      type: 'address',
      value: '0x10ed43c718714eb63d5aa57b78b54704e256024e'
    },
    { name: 'amount0In', type: 'uint256', value: '0' },
    {
      name: 'amount1In',
      type: 'uint256',
      value: '1202473582518654197'
    },
    {
      name: 'amount0Out',
      type: 'uint256',
      value: '777540000000000000000'
    },
    { name: 'amount1Out', type: 'uint256', value: '0' },
    {
      name: 'to',
      type: 'address',
      value: '0x431731d312dffa688a37d81af8874a58776eacfd'
    }
  ],
  address: '0x3D2Bcc3Ec4f97b0d4209Fd947FC70F666F39D995'
}

Answer 1

If you're using the Web3 library you can instantiate the pair contract (0x3D2Bcc3Ec4f97b0d4209Fd947FC70F666F39D995) by providing its ABI and address (you can get the ABI via BSCScan API).

Then, just call the token1 and token2 methods and you'll get the addresses of the ERC20 tokens. You can see those methods and what they return here on BSCScan.

Ie.:

// Hardcode the ABI or get it via API (eg.: via BSCScan API)
const abi = {};

// Instantiate the contract
const contract = new web3.eth.Contract(abi, '0x3D2Bcc3Ec4f97b0d4209Fd947FC70F666F39D995')

// Get the addresses of the pair's tokens
const [token1Addr, token2Addr] = await Promise.all([
  contract.methods.token1().call(),
  contract.methods.token2().call()
]);

// From here you can instantiate the token contracts and
// call their `symbol()` method to find out what they are