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Hi I'm trying to interact with an Ethereum smart contract from my node js api.

My controller function is as follows:

var web3 = require('web3');

module.exports.getTokenBalance = function(req, res) {
var abi = //long ABI
var MyContract = web3.eth.contract(abi);

  // initiate contract for an address
  var myContractInstance = MyContract.at('...');
  myContractInstance.balanceOf.call('addr', function(err, data) {

  }
}

I'm using the web3@0.20 package. When I try to call this API function I get the following error :

"Cannot read property 'contract' of undefined."

Am I missing something stupid?

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1 Answer 1

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require('web3') returns a class. You need to instantiate it first. Note the capital W:

var Web3 = require('web3');
var web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:8545'));
// (or some other provider)

// web3.eth.contract should work down here.
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  • Ok cool. Another thing is, I'd like to somehow have a Eth node running on a heroku server so I can send transactions there from my api. Is this a sensible thing to do?
    – SwimmingG
    Jan 14, 2018 at 8:36
  • Seems like an unrelated question, so it might be better to ask it as such. But I do want to make sure you're aware of existing public nodes like Infura.
    – user19510
    Jan 14, 2018 at 8:38
  • What a fantastic resource. Thanks I'll take a look into it.
    – SwimmingG
    Jan 14, 2018 at 8:52

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