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I want to fetch certain transaction logs from a local ethereum node. For that, I need to identify how to differentiate between ERC 20 and ERC 721 transaction receipts. From what I saw on Etherscan, i couldn't find any differentiating method as both the receipts look similar. The link of an ERC 20 transaction receipt is here https://etherscan.io/tx/0xbad497f6d96dd111c221ce41355cbb9ac912a6c0953ccb94113ba8232ab95e0a and ERC 721 transaction receipt is https://etherscan.io/tx/0x1ae8ba8417d6603e4f0b930b768814883af2d0ee091bc78145e871171768710e.

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Here is the Transfer event prototype on each standard:

  • ERC20: event Transfer(address, address indexed _to, uint256 _value)
  • ERC721: event Transfer(address, address indexed _to, uint256 indexed _tokenId)

These two signatures are indeed the same when you hash them for the purpose of locating Transfer events in the ledger using (for example):

receipt.topics[0] == Web3.utils.keccak256("Transfer(address,address,uint256)")

However, note that each one of them has a different number of indexed parameters.

Therefore, you can determine if a transfer receipt is ERC20 or ERC721 as follows:

  • ERC20: receipt.topics.length == 1
  • ERC721: receipt.topics.length == 2
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