web3 error - web3.eth.Contract is not a constructor

Question

i try to get the contract balance and im using this

var Web3 = require('web3')
var web3 = new Web3('ropsten.infura.io/v3/123456789')
var abi = abi is here ;

var contractAddress = '0x31111.....';
var contract = new web3.eth.Contract(abi, contractAddress);
//var address = '0x31111......';

web3.eth.getBalance(contract.address, function (e, r) {
   $('contractBalanceAgi').text(convertWeiToEth(r).toFixed(4))
 })

and when running this i get following error in my console web3.eth.Contract is not a constructor

when i googled for it some said its because of the new web3 js version but the new web3 version requires this var contract = new web3.eth.Contract(abi, contractAddress) new and capital C

Answer 1

I'm not sure if this is the cause of your issue but I am fairly sure that you need to include the protocol prefix in the URL provided to the web3 constructor:

var web3 = new Web3('ropsten.infura.io/v3/123456789')

Should include the protocol:

var web3 = new Web3('https://ropsten.infura.io/v3/123456789')

(P.S. please don't use var, const is fairly appropriate)