Uniswap/Pancakeswap Get received tokens from a transaction receipt

[benwilliamson86]

Uniswap/Pancakeswap docs say that swapexacttokensfortokens() function will return The input token amount and all subsequent output token amounts.

How can i access this value so that i can use it to swap the exact tokens i receive back? I see from the transaction receipt there is a tx.data that may hold this information but i don't know how to make it readable/usable so i can insert it back into the function.

Many Thanks.

[zemse]

@benwilliamson86 You can get the information from receipt.logs. Whenever a swap takes place, it emits multiple events. You have to find the Uniswap's Swap event among them.

const swapEventTopic = ethers.utils.id('Swap(address,uint256,uint256,uint256,uint256,address)')

// discard all other logs
const swapLogs = receipt.logs.filter(log => log.topics[0] === swapEventTopic);

// take the last swap event
const lastSwapEvent = swapLogs.slice(-1)[0]

// decode the data
const swapInterface = new ethers.utils.Interface(['event Swap (address indexed sender, uint256 amount0In, uint256 amount1In, uint256 amount0Out, uint256 amount1Out, address indexed to)'])
const parsed = swapInterface.parseLog(lastSwapEvent);

// use the non zero value
const receivedTokens = parsed.args.amount0Out.isZero() ?  parsed.args.amount1Out : parsed.args.amount0Out;

[rafaelfaria]

Legend @zemse !!!!

now receivedTokens is a bignumber.

when i do receivedTokens.toString() I get "539185737174088139"

which by looking at the transaction, looks almost close to the right amount

0.539185737174088139 ($0.54)

What is the best way to format it?

[rafaelfaria]

Found it! :P
Number(ethers.utils.formatEther(receivedTokens))

[zemse]

You need to know the decimals of the token.

ethers.utils.formatUnits(receivedTokens, 18); // gives a string `0.539185737174088139`

Usually decimals of ERC20 tokens is 18. But it can be something else like 6 for USDC, USDT, Or 8 for WBTC. Or even 27 for SHIB. To know the decimals of a token programmatically, you would need an ERC20 interface.

const tokenContract = new ethers.Contract(tokenAddress, ['function decimals() external view returns (uint8)'], provider);
const decimals = await tokenContract.decimals(); // 18 or 6 or whatever

ethers.utils.formatUnits(receivedTokens, decimals);

[rafaelfaria]

@zemse that's right. I implemented that too. Thanks for calling that out.

[maciejmoczulski]

The received token amount from logs is different in comparison to MetaMask.
I guess that this might be related to Tax. Is there any possibility to receive the amount of tokens with tax applied?

[christ662]

Bonsoir comment vous allez vraiment j'ai besoin d'aide si vous plaît