Programmatically access deployed ERC20PresetMinterPauserUpgradeSafe


I followed your docs and managed to advance quite a bit. I got stuck while trying to programmatically access the ERC20PresetMinterPauserUpgradeSafe I deployed as is, following the instructions here:

So far I only tested programmatically the sample Box contract, which I compiled and deployed. But since I am deploying an instance of ERC20PresetMinterPauserUpgradeSafe there is no reference to this at the build folder and thus the way that I was accessing the contract programmatically via loader.fromArtifact is not working anymore and I am getting this error when running a similar code that I used for the Box contract:

   at Object.openSync (fs.js:462:3)
   at Object.readFileSync (fs.js:364:35)
   at Object.readFileSync (/home/luis/token/node_modules/jsonfile/index.js:61:22)
   at loadArtifact (/home/luis/token/node_modules/@openzeppelin/contract-loader/lib/index.js:47:23)
   at Web3Loader.BaseLoader.fromArtifact (/home/luis/token/node_modules/@openzeppelin/contract-loader/lib/index.js:65:18)
   at main (/home/luis/token/src/index.js:14:26)
   at Object.<anonymous> (/home/luis/token/src/index.js:38:1)
   at Module._compile (internal/modules/cjs/loader.js:1137:30)
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:1157:10)
   at Module.load (internal/modules/cjs/loader.js:985:32)
   at Function.Module._load (internal/modules/cjs/loader.js:878:14)
   at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
   at internal/main/run_main_module.js:17:47
(node:318) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see (rejection id: 1)
(node:318) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

In summary what I need is a code example of how to access this contract in this situation where I did not compile it myself.

I am running Ubuntu 20.04 LTS

:1234: Code to reproduce

const token = loader.fromArtifact('ERC20', address);


1 Like

Hi @Luis-Fernando-Molina,

Welcome to the community :wave:

I deployed the preset contract as an upgradeable contract using the already deployed implementation contract.

$ npx oz deploy @openzeppelin/contracts-ethereum-package/ERC20PresetMinterPauserUpgradeSafe
No contracts found to compile.
? Choose the kind of deployment upgradeable
? Pick a network rinkeby
✓ Linked dependency @openzeppelin/contracts-ethereum-package 3.0.0
All implementations are up to date
? Call a function to initialize the instance after creating it? Yes
? Select which function initialize(name: string, symbol: string)
? name: string: My Token
? symbol: string: TKN
✓ Setting everything up to create contract instances
✓ Instance created at 0x4f78cC83EF5cA802C7F3AaC9865Ad77E0732360e
To upgrade this instance run 'oz upgrade'

To get the precompiled artifacts, I copied them from node_modules

$ cp node_modules/@openzeppelin/contracts-ethereum-package/build/contracts/*

We can then interact programmatically (following instructions in the documentation:
Using the address of the proxy contract.

// src/index.js
const Web3 = require('web3');
const { setupLoader } = require('@openzeppelin/contract-loader');

const { projectId, mnemonic } = require('../secrets.json');

const HDWalletProvider = require('@truffle/hdwallet-provider');

const provider = new HDWalletProvider(mnemonic, `${projectId}`);

async function main() {
  // Set up web3 object
  const web3 = new Web3(provider);

  // Set up a web3 contract, representing a deployed ERC20, using the contract loader
  const address = '0x4f78cC83EF5cA802C7F3AaC9865Ad77E0732360e';
  const loader = setupLoader({ provider: web3 }).web3;
  const token = loader.fromArtifact('ERC20PresetMinterPauserUpgradeSafe', address);

  // Retrieve accounts
  const accounts = await web3.eth.getAccounts();

  console.log(`Account: ${accounts[0]}`);

  // Call the deployed token contract
  const name = await;
  const symbol = await token.methods.symbol().call();
  const decimals = await token.methods.decimals().call();
  const totalSupply = await token.methods.totalSupply().call();
  console.log(`${name} (${symbol}) - Decimals:${decimals} Total Supply:${totalSupply}`);

  // At termination, `provider.engine.stop()' should be called to finish the process elegantly.


The output of this script is:

$ node src/index.js
Account: 0xEce6999C6c5BDA71d673090144b6d3bCD21d13d4
My Token (TKN) - Decimals:18 Total Supply:0

Hi @abcoathup !

I am happy to be part of the community. Thanks for the detailed explanation. That was all I needed. I will move forward now and see how far I can get.


1 Like

Hi @Luis-Fernando-Molina,

Great to hear! Feel free to ask all the questions that you need.

If you have a moment it would be great if you could introduce yourself.