部署智能合约时出错，无法读取未定义的“已部署”属性？

Question

Im making a frontend for a Dapp, so after making instances of the smart contracts and setting a provider I try to deploy the contract, get the token balance and display it in on the web page but get the error: Cannot read property 'deployed' of undefined in my browser.

Note that my FixedSupplyToken.sol is deployed on test RPC as I can see in the FixedSupplyToken.json file, it has an address. Was thinking this was the issue, but no such luck...

app.js:

    // Import libraries we need.
    import { default as Web3} from 'web3';
    import { default as contract } from 'truffle-contract'
    
    // Import our contract artifacts and turn them into usable abstractions.
    import exchange_artifacts from '../../build/contracts/Exchange.json'
    import token_artifacts from '../../build/contracts/FixedSupplyToken.json'
    
    
    var accounts;
    var account;
    
    var ExchangeContract = contract(exchange_artifacts);
    var TokenContract = contract(token_artifacts);
    window.App = {
      start: function() {
       //bootstrap everything
       
       ExchangeContract = web3.setProvider(web3.currentProvider);
       TokenContract = web3.setProvider(web3.currentProvider);

},

 //update balance function

 updateTokenBalance: function() {
    var tokenInstance;
    **TokenContract.deployed().then(function (instance) { // getting the Uncaught TypeError: Cannot read property 'deployed' of undefined**
        tokenInstance = instance;
        return tokenInstance.balanceOf.call(account);
    }).then(function (value) {
        
        var balance_element = document.getElementById("balanceTokenInToken");
        balance_element.innerHTML = value.valueOf();
    }).catch(function (e) {
        console.log(e);
        App.setStatus("Error getting balance; see log.");
    });
  },

So I have tried :

Even if I uncomment web3.setProvider(web3.currentProvider) I get the setProvider undefined error.

Thanks for any feedback :)

Answer 1

In the start function, you're reassigning the TokenContract variable.

Try changing

ExchangeContract = web3.setProvider(web3.currentProvider);
TokenContract = web3.setProvider(web3.currentProvider);

to:

ExchangeContract.setProvider(web3.currentProvider);
TokenContract.setProvider(web3.currentProvider);

Edit based on comment:

The root of the problem is that web3.setProvider method returns void or undefined , so in the statement TokenContract = web3.setProvider(web3.currentProvider); you are assigning undefined to TokenContract , hence the error. Setting the web3 provider and the Truffle contract provider are two different actions. Not sure if there's more code in the //bootstrap everything but if for some reason you need to set the provider explicitly try changing the code to:

web3.setProvider(web3.currentProvider);
ExchangeContract.setProvider(web3.currentProvider);
TokenContract.setProvider(web3.currentProvider);

The first line, though, shouldn't be necessary if Web3 is configured correctly. I suggest reading this article for this since there's been changes in how this is done: https://medium.com/@awantoch/how-to-connect-web3-js-to-metamask-in-2020-fee2b2edf58a .

The gist of it is:

window.web3 = new Web3(window.ethereum);
window.ethereum.enable();

Answer 2

This line:

import token_artifacts from '../../build/contracts/FixedSupplyToken.json'

I'm guessing your local webserver is rooted where your HTML page is. Hence, any attempt to pull content outside of the web server root (ie from the .. folder) is going to get declined.

Reload your page with the the F12 tools running showing network traffic. I suspect you're going to get a 404 result when the page attempts to do a GET ../../build/contracts/FixedSupplyToken.json

Hence, token_artifacts undefined, and everything else created off of it is also undefined.

The quick hack is to move FixedSupplyToken.json into your web root and adjust the import statement appropriately.

The other issue I had with my python web server with that even after I had moved the json to the web root, the python -m http.server thing I was running was returning a mime type in the Content-Type header rejected by the javascript importer. The quick hack I did was just to paste the json declaration into a .js file and give it a variable assignment such as the following:

window.FizzBuzzContract =    // added this line
{
  "contractName": "FizzBuzz",
  "abi": [...