Web3.js Type Error – Resolving web3.eth.Contract Not a Constructor Issue

contract-developmentweb3js

Why can't I instantiate my smart contract?

When I try and instantiate an instance of a smart contract with the following code…

let contractInstance = new web3.eth.Contract(abi, '0x6c6101607c84368dd130909bae7c7273d8914708');

… I get the following Error:

Uncaught TypeError: web3.eth.Contract is not a constructor

This is confusing to me because when I use web3.version in my console, it returns 1.0.0-beta.36. I instantiated my web3 provider in the following way:

window.addEventListener('load', async () => {
if (typeof web3 !== 'undefined') {
    web3 = new Web3(web3.currentProvider);
    console.log('MetaMask Success');
    await window.ethereum.enable();
    web3.eth.defaultAccount = web3.eth.accounts.givenProvider.selectedAddress;

} else {
    console.log('No web3? You should consider trying MetaMask!');
    web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:7545'));
}
});

Any suggestions?

Best Answer

In app.js you are initializing contractInstance outside of the 'load' event.

window.addEventListener('load', async () => {
    // ...
});

web3.eth.defaultAccount = web3.eth.accounts.givenProvider.selectedAddress;
contractInstance = new web3.eth.Contract(abi, '0x15013d783fadAaA9e9d2F0e8d71C575f81a39834'); // Ganache contract address ''0x15013d783fadAaA9e9d2F0e8d71C575f81a39834''

Due to the async nature of the web it is possible app.js code is executed before the load event is triggered. Make sure to initialize the contract after the load event was fired.

window.addEventListener('load', async () => {
    // ...



    web3.eth.defaultAccount = web3.eth.accounts.givenProvider.selectedAddress;
    contractInstance = new web3.eth.Contract(abi, '0x15013d783fadAaA9e9d2F0e8d71C575f81a39834'); // Ganache contract address ''0x15013d783fadAaA9e9d2F0e8d71C575f81a39834''
});

Related Solutions

[Ethereum] ‘Error: base fee exceeds gas limit’ When creating new contract instance (Using Truffle, Web3Js and testrpc)

Since your example code uses truffle-contract you can specify the default values for your transactions and contract deployments like this (Conferrence is the name of your contract. I used the truffle default values):

Conferrence.defaults({
  from: account,
  gas: 4712388,
  gasPrice: 100000000000
})

I had the same problem (base fee exceeds gas limit) and browser-solidity gave me a Gas requirement of function xyz.sol:Xyz.doSomething(address) unknown or not constant. Specifying default values helped eventually.

[Ethereum] How to get events result using web3 1.0.0 version

You have to take care of following things:

Use websocket provider in order to subscribe to events in web3.js 1.0. For example, if you are using local TestRPC then instantiate the web3 as by using your websocket port (here in this case its 8545):
```
const web3 = new Web3(Web3.givenProvider || "ws://127.0.0.1:8545");
```

The example code for myContract having an event of MyEvent will be like:

myContract.events.MyEvent ({
  fromBlock: 'latest',
  toBlock: 'latest'
}, function(error, result) {
  if (!error) {
    console.log(result);
  } else {
    console.log(error);
  }
});

Note: in the above block of code, I'm watching for the events in 'latest' block mined. The reason is, this block of code is the same as we have watch method in the older version. This will only watch for events that are not fired yet. If you want to get all the events, you have to use getPastEvents:

    myContract.getPastEvents('MyEvent', {
      fromBlock: 0,
      toBlock: 'latest'
    }, function(error, result) {
      if (!error) {
        console.log(result);
      } else {
        console.log(error);
      }
    });

For more details, see the Docs

Best Answer

Related Solutions

[Ethereum] ‘Error: base fee exceeds gas limit’ When creating new contract instance (Using Truffle, Web3Js and testrpc)

[Ethereum] How to get events result using web3 1.0.0 version

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