I need to decode transaction input on the client side. Libraries like ethereum-input-data-decoder needs NodeJS dependencies like fs.

Now I decode the one type of contract methods as follows:

const getERC20TransferByHash = async (hash) => {
  const tx = await web3.eth.getTransaction(hash)
  if (
    tx !== null &&
    (tx.input.length === 138 || tx.input.slice(2, 10) === 'a9059cbb')
  ) {
    const receiver = web3.utils.toChecksumAddress('0x' + tx.input.slice(34, 74))
    const amount = web3.utils.toBN('0x' + tx.input.slice(74))
    const contractAddress = tx.to
    const sender = web3.utils.toChecksumAddress(tx.from)
    return { receiver, amount, contractAddress, hash, sender }
  return {}

Decoding by web3.utils.toAscii(transaction.input) also don't work.

Is there a single way to make it easy?


Can you try decodeParameters? Like:

const erc20TransferABI = [{
        type: "address",
        name: "receiver"
        type: "uint256",
        name: "amount"
const decoded = web3.eth.abi.decodeParameters(
    tx.input.slice(10)); // Or (11), not sure

Even perhaps, take erc20TransferABI from the ABI file itself.

  • The first 10 bytes is the signature function? Oct 4 '21 at 19:56
  • The first 4 bytes, which appear as 8 characters when represented as a string. Then if you also need to remove "0x" from the string, then that makes 10 characters to remove in all. Oct 5 '21 at 9:09
  • Update the answer.Instead of objects with keys name and type, you need paste array with types as string (address, uint256). Oct 5 '21 at 9:42
  • What version of Web3 are you using? Perhaps this array or detailed object way for the ABI could be due to versions. Oct 5 '21 at 13:48

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