How do I get a signed transaction without sending it to the chain?

Question

I'm using ethers.js to interact with a contract. When I call a method of my contract, i.e const txn = await someContract.someMethod(...data).

It returns a signed transaction and also sends it to the chain which I'd like to avoid cause I want to replay it on a local fork. I tried populateTransaction and signTransaction but there'll be some missing information if you do it this way.

Answer 1

You can create a transaction (without sending it) like this using web3js:

    const web3Provider = new Web3(
      new Web3.providers.Web3Provider(
        ENDPOINT
      )
    )
    web3Provider.eth.accounts.wallet.add(WALLET_KEY)

    const contract = new web3Provider.eth.Contract(
      ABI,
      CONTRACT_ADDRESS
    )


    const trx = contract.methods.METHOD_NAME(...params)

    const gas = await trx.estimateGas({ from: WALLET_ADDRESS })
    console.log('gas :>> ', gas)
    const gasPrice = await provider.eth.getGasPrice()
    console.log('gasPrice :>> ', gasPrice)
    const data = trx.encodeABI()
    console.log('data :>> ', data)
    const nonce = await provider.eth.getTransactionCount(WALLET_ADDRESS)

    console.log('nonce :>> ', nonce)

    const trxData = {
      from: WALLET_ADDRESS,
      to: CONTRACT_ADDRESS,
      data,
      gas,
      gasPrice,
      nonce,
    }

    console.log('Transaction ready to be sent')
    // actually send the transaction now 👇
    const receipt = await provider.eth.sendTransaction(trxData)
    console.log(`Transaction sent, hash is ${receipt.transactionHash}`)

Just adapt the wallet address, contract, method and params