Metamask: Logging user on web3.js is calling a function before web3 is assigned

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Metamask: User logging into web3.js is calling a function before web3 is assigned

As a developer building blockchain applications with React, you’re probably familiar with setting up Web3.js for secure, decentralized interactions. However, sometimes issues arise that can make debugging difficult. In this article, we’ll explore the cause of a Metamask user registration issue with web3.js.

The Problem: User Registration Before Web3 Is Assigned

When building a React application for your blockchain project, it’s standard practice to set up the MetaMask integration before initializing any components. This ensures that users can log in and interact with your app securely.

Here’s an example of how you might initialize MetaMask in your React component:

import MetaMask from '@metamask-connect/express';
import Web3 from 'web3';
const Application = () => {
const [web3, setWeb3] = useState(null);
// Initialize Web3.js with MetaMask integration
useEffect(() => {
setWeb3(new Web3(window.ethereum));
}, []);
if (!web3) {
console.error('Error initializing web3');
}
return (
{web3 ? (
 logUserOnWeb3(web3)}>Log user on web3
) : (
Loading…
)}
);
};

In this code snippet, we initialize Web3.js with the MetaMask integration using the useEffect hook. The setWeb3 function is called when the component is mounted and updates the web3 state variable.

The problem: User registration before Web3 is assigned

Now, let’s say you’ve created your React application without setting up the MetaMask integration yet. When you reload the page, you might see a message in the console that says “Error initializing web3”. This could be because the web3 state variable hasn’t been updated yet.

However, when you call getNfts() in the component, it tries to register the user on Web3.js before the web3 state variable has been initialized. As a result, the getNfts() function is called with an empty or undefined web3 object, resulting in errors.

Troubleshooting: Make sure MetaMask is integrated before initializing Web3

To resolve this issue, you need to make sure MetaMask integration is complete before initializing Web3.js. Here are some possible solutions:

• Wait for MetaMask to load: You can use the window.ethereum object to wait for MetaMask to load and become available before initializing Web3.js.

import { window } from 'web3-utils';
const [web3, setWeb3] = useState(null);
useEffect(() => {
const onMetaMaskLoaded = () => {
if (window.ethereum) {
setWeb3(new Web3(window.ethereum));
}
};
// Wait for MetaMask to load
window.onLoad(onMetaMaskLoaded);
}, []);

• Check MetaMask integration

  : You can add a simple check to check if MetaMask integration is complete before initializing Web3.js.

import MetaMask from '@metamask-connect/express';
import Web3 from 'web3';
constant Application = () => {
const [metaMaskLoaded, setMetaMaskLoaded] = useState(false);
useEffect(() => {
// Check if MetaMask is loaded and integrated
window.ethereum.on('conti', (conti) => {
setMetaMaskLoaded(true);
});
}, []);
return (
{ metaMaskLoaded && (
 logUserOnWeb3(web3)}>Log user on web3
)}
);
};

Implementing one of these solutions should fix the issue and log users correctly on Web3.js after initializing the MetaMask integration.