How get estimated gas before sending the transaction?

Question

How do you get the "estimated gas" from a "swapExactETHForTokens" function? As shown in metamask (before one can accept the purchase)

Binance Smart Chain (BSC)

From the pancakeswap contract ( https://bscscan.com/address/0x10ed43c718714eb63d5aa57b78b54704e256024e#writeContract ) in function number 10 you can buy tokens using "swapExactETHForTokens" and in function number 14 you can sell tokens using "swapExactTokens"

When you try to make a transaction when you want to buy or sell and it is not possible to proceed with that, then it appears that the gas fee expense is "0.3" or "0.4", which indicates that there is an error (and obviously one does not have to accept)

In this example it is because I try to buy tokens when there is NOT a defined price in the token / it has no liquidity in BNB, therefore the 0.3 bnb gas fee is displayed (error)

I have automated "buy" and "sell" through a BOT, which, using the functions mentioned above, helps me to carry out these processes. How do I get this value of the "estimated gas" as shown in the example in "Metamask"? but using web3 or ethers!

I tried "estimateGas" in ethers, but it returns a normal gas value, and not the same as in the example with metamask of 0.3 bnb

    let test = async () => {
const provider_ = new ethers.providers.WebSocketProvider(data.Wss_Nodo); //Nodo Private
let tokenAbi_ = [{"inputs":[{"internalType":"string","name":"_name","type":"string"},{"internalType":"string","name":"_symbol","type":"string"},{"internalType":"uint256","name":"_decimals","type":"uint256"},{"internalType":"uint256","name":"_supply","type":"uint256"},{"internalType":"uint256","name":"_txFee","type":"uint256"},{"internalType":"uint256","name":"_burnFee","type":"uint256"},{"internalType":"uint256","name":"_charityFee","type":"uint256"},{"internalType":"address","name":"_FeeAddress","type":"address"},{"internalType":"address","name":"tokenOwner","type":"address"}],"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":"previousOwner","type":"address"},{"indexed":true,"internalType":"address","name":"newOwner","type":"address"}],"name":"OwnershipTransferred","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"},{"inputs":[],"name":"FeeAddress","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"_BURN_FEE","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"_CHARITY_FEE","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"_TAX_FEE","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"_owner","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"_value","type":"uint256"}],"name":"burn","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"decimals","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"subtractedValue","type":"uint256"}],"name":"decreaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tAmount","type":"uint256"}],"name":"deliver","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"excludeAccount","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"includeAccount","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"addedValue","type":"uint256"}],"name":"increaseAllowance","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"isCharity","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"isExcluded","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"mint","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"owner","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tAmount","type":"uint256"},{"internalType":"bool","name":"deductTransferFee","type":"bool"}],"name":"reflectionFromToken","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"renounceOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"setAsCharityAccount","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"rAmount","type":"uint256"}],"name":"tokenFromReflection","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalBurn","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalCharity","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalFees","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"sender","type":"address"},{"internalType":"address","name":"recipient","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"_txFee","type":"uint256"},{"internalType":"uint256","name":"_burnFee","type":"uint256"},{"internalType":"uint256","name":"_charityFee","type":"uint256"}],"name":"updateFee","outputs":[],"stateMutability":"nonpayable","type":"function"}];
const address_ = "0x3A7bf1305D0561b4E0363E6a262096c77C7CB5Db"; //My Wallet Test
const erc20 = new ethers.Contract(address_, tokenAbi_, provider_);

const recipient = "0x36953b5ec00a13edceceb3af258d034913d2a79d"; //Token Test
const estimation = await erc20.estimateGas.transfer(recipient, 100);
console.log(estimation) // BigNumber { _hex: '0x5444', _isBigNumber: true } (21572)
}

Obviously I'm doing it wrong:( A help please !!

Answer 1

i am using web3 to estimate gas it works only when I am transferring tokens from wallet to another but when testing it on minting I get error:

let estimated_gas = await web3.eth.estimateGas({
        'from': WalletAddress,
        'to': ContractAddress,
        'value': web3.utils.toHex(web3.utils.toWei('0.0035', 'ether')),
        'data': contract.methods.mint.encodeABI(),
        "gasPrice": web3.utils.toHex(gas_fee),
    });

and I get this error:

Error: Returned error: execution reverted: Value below required mint fee for the amount

not sure what I am doing wrong

Answer 2

To make a swap you must estimateGas for a Swap, and not for a transfer as you did!