Web3.js Node.js – Fix TypeError: Web3 is not a Constructor When Using Node.js with Truffle-Contract

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I'm trying to use node.js with my smart contract for my app. As I've tried to convert from using the default app.js set-up to index.js set-up I've ran into this weird issue I can't fix.

It throws the error when trying to instantiate my .json file with truffle-contract.

App.contracts.Flip = TruffleContract(FlipArtifact); //at this line it goes to truffle-contract.js and throws this error: 

var BigNumber = (new Web3()).toBigNumber(0).constructor;

TypeError: Web3 is not a constructor

I had the exact same thing but in my app.js where truffle puts it automatically and it was working fine.

Could someone please explain the difference between using truffle-contract in my app.js/client-side and my index.js/server-side. Thanks for any help.

Best Answer

If you're running in a browser with MetaMask, then Web3 is injected as a side effect of this (although try not to rely on this behaviour). In server-side code, you must import web3 yourself, by putting something like:

const Web3 = require('web3')

near the start of your code. You may also have to npm install web3 or yarn install web3, and if you're using BigNumber (which they no longer bundle with Web3 1.0) then you probably want to specify npm install web3@^0.20.6 or yarn install web3@^0.20.6.

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I am able to reproduce issue that you were facing. I did following to solve this issue. Created two separate contract files inside contracts folder for SimpleStore and ContrctFactory as following :- SimpleStore.sol file -

pragma solidity ^0.4.16;

contract SimpleStore {
    uint public value;
    function SimpleStore (uint num) public {
        value = num;
    }

    function setValue (uint num) public {
        value = num;
    }
}

ContractFactory.sol file -

pragma solidity ^0.4.16;

contract SimpleStore {
    uint public value;
    function SimpleStore (uint num) public {
        value = num;
    }

    function setValue (uint num) public {
        value = num;
    }
}
contract ContractFactory {

    address public store;

    function ContractFactory () public {

    }

    function createStore () public {
        store = new SimpleStore(12);
    }
}

2_deploy_contracts.js file -

var SimpleStore = artifacts.require("./SimpleStore.sol");
var ContractFactory = artifacts.require("./ContractFactory.sol");
module.exports = function(deployer) {
  deployer.deploy(SimpleStore,10, {gas: 6700000});
  deployer.deploy(ContractFactory,{gas: 6700000});
};

app.js file -

import { default as Web3} from 'web3';
import { default as contract } from 'truffle-contract'
import SimpleStore_artifacts from '../../build/contracts/SimpleStore.json'
import ContractFactory_artifacts from '../../build/contracts/ContractFactory.json'

var SimpleStore = contract(SimpleStore_artifacts);
var ContractFactory = contract(ContractFactory_artifacts);
$( document ).ready(function() {
  if (typeof web3 !== 'undefined') {
    console.warn("Using web3 detected from external source like Metamask")
    // Use Mist/MetaMask's provider
    window.web3 = new Web3(web3.currentProvider);
  } else {
    console.warn("No web3 detected. Falling back to http://localhost:8545. You should remove this fallback when you deploy live, as it's inherently insecure. Consider switching to Metamask for development. More info here: http://truffleframework.com/tutorials/truffle-and-metamask");
    // fallback - use your fallback strategy (local node / hosted node + in-dapp id mgmt / fail)
    window.web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));

  }
  SimpleStore.setProvider(web3.currentProvider);
  ContractFactory.setProvider(web3.currentProvider);
  ContractFactory.deployed().then(function(instance) {
    return instance.createStore({from: web3.eth.accounts[0],gas: 6700000}); 
    console.log("******");
  });
});

Adding gas cost as an argument has resolved problem of VM exception.

instance.createStore({from: web3.eth.accounts[0],gas: 6700000});

I am also able to execute transaction from truffle console -

truffle(development)> ContractFactory.deployed().then(function (instance) { return instance.createStore({from: web3.eth.accounts[0],gas: 6700000});})
{ tx: '0x4d34e45cddbfa6f087f5dcb02bb5e7dc0fa18a0f7d24e87f8fff8702dd3e53bc',
  receipt: 
   { transactionHash: '0x4d34e45cddbfa6f087f5dcb02bb5e7dc0fa18a0f7d24e87f8fff8702dd3e53bc',
     transactionIndex: 0,
     blockHash: '0xf77b2baa3cacc941a8376376425c642c6db580e4a26918a0905ed589a618bfe7',
     blockNumber: 26,
     gasUsed: 123078,
     cumulativeGasUsed: 123078,
     contractAddress: null,

Best Answer

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