How to detect if an Ethereum address is an ERC20 token contract?

Question

If I only get an Ethereum address from the input, is there a way to find out whether it matches the ERC20 token standard?

Answer 1

ERC165 tackles this problem, but, unfortunately, most ERC20 implementations don't support it (as of Nov 2018, at least OpenZeppelin doesn't). This means that you could try calling the supportsInterface function, but it would revert anyway and you'd rather complicate things.

Nevertheless, here's how it's defined in ERC721:

bytes4 private constant _InterfaceId_ERC721 = 0x80ac58cd;
/*
 * 0x80ac58cd ===
 *   bytes4(keccak256('balanceOf(address)')) ^
 *   bytes4(keccak256('ownerOf(uint256)')) ^
 *   bytes4(keccak256('approve(address,uint256)')) ^
 *   bytes4(keccak256('getApproved(uint256)')) ^
 *   bytes4(keccak256('setApprovalForAll(address,bool)')) ^
 *   bytes4(keccak256('isApprovedForAll(address,address)')) ^
 *   bytes4(keccak256('transferFrom(address,address,uint256)')) ^
 *   bytes4(keccak256('safeTransferFrom(address,address,uint256)')) ^
 *   bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)'))
 */

Although it's not guaranteed for all implementations to define the interface id, there's a higher chance it will work in the case of ERC721, given the fact the community agreed on applying ERC165 right from the get-go. If the return value of the query below is true, then it means you have a compliant contract, otherwise just revert the transaction.

// you can call this in your contracts
IERC721(contractAddress).supportsInterface(0x80ac58cd)

Also, a useful resource for manually checking the bytes4 of a given method is 4byte.directory

Answer 2

If you are asking about off-chain, so use these functions:

getContract(url, smartContractAddress){
    const Web3Eth = require('web3-eth');

    const abi_ = this.getABI();
    const web3Eth = new Web3Eth(Web3Eth.givenProvider || url);
    return new web3Eth.Contract(abi_, smartContractAddress);
}

async getERCtype(contract){
    const is721 = await contract.methods.supportsInterface('0x80ac58cd').call();
    if(is721){
        return "ERC721";
    }
    const is1155 = await contract.methods.supportsInterface('0xd9b67a26').call();
    if(is1155){
        return "ERC1155";
    }
    return undefined;
}

getABI(){
    return [         
        {"constant":true,"inputs": [
                {"internalType":"bytes4","name": "","type": "bytes4"}],
            "name": "supportsInterface",
            "outputs": [{"internalType":"bool","name": "","type": "bool"}],
            "payable": false,"stateMutability":"view","type": "function"}         
    ];
}

like this:

const contract = getContract(url, smartContractAddress);
const type = await getERCtype(contract);
console.log(type);