Get ERC721 token total supply using web3.js

Question

I created a simple contract which basically does nothing but mints new ERC721 tokens. The solidity code for it is as follows:

struct Monster {
        string name;
        uint level;
        uint attackPower;
        uint defensePower;
    }

Monster[] public monsters;
function createToken(string _name, address _to) public{
        require(owner == msg.sender);
        uint id = monsters.length;
        monsters.push(Monster(_name, 1, 100, 100));
        _mint(_to, id);
    }

I invoked the createToken method serveral times and created a token named testToken and sent it to my metamask wallet account. I can see the token in metamask. The contract is deployed on ropsten network and I have the contract address.

Now, I want to use web3.js to simply check this balance from my account (metamask wallet). I am trying to use this library https://www.npmjs.com/package/erc721 for the abi.

I have the following code:

const { MintableNonFungibleToken } = require('erc721');
var abi = MintableNonFungibleToken;
var contractAddress = '0x17b95748b3da7f1c4fbf665b8340b851cec7b856';
var token = web3.eth.contract(abi).at(contractAddress);
console.log(token.balanceOf(address).toNumber()); 

I get the correct token count here. However, I could not find any method token.decimals() like in ERC20 contract.

1. Does it mean I can just use token.balanceOf(address).toNumber() to find the token count?
2. How do I identify the tokenId of these tokens so I can query more information about the token?
3. How do I execute totalSupply()? I tried token token.totalSupply().toNumber(). However, the value is always 0.

PS: I haven't implemented totalSupply(). I am trying to write generic APIs to query ERC721 contracts and get information, so I am looking for something from standard specs from ERC721 instead of depending on the developer to write specific functions in contracts.

Answer 1

A compliant ERC-721 token will have a totalSupply method implemented, eg

function totalSupply() public view returns (uint) {
    return monsters.length;
}

Your contract will need to implement that method to comply with the spec