Integrating web3 from Metamask in React

Question

I am new to ReactJS. Seem to be having trouble integrating web3 from Metamask in React. Metamask version: web3@1.0.0-beta.34

import Web3 from 'web3'

let web3;

window.addEventListener('load', function () {
    if (typeof window.web3 !== 'undefined') {        
        web3 = new Web3(window.web3.currentProvider);
    } else {
        // No web 3 provider
        console.log("Please install Metamask");
    }    
});

export default web3;

Getting the following error:

window is not defined
ReferenceError: window is not defined
at Object../lib/getWeb3.js (lib/getWeb3.js:5:0)

Answer 1

window is not defined on Server, only in client's browser, hence you can't use MetaMask server-side. However, you can connect to INFURA when you want to use web3 in your React component server-side or without MetaMask support.

The simplest way is to use react-web3-provider component.

Add the Web3Provider to your root React component:

import Web3Provider from 'react-web3-provider';

ReactDOM.render(
    <Web3Provider
        defaultWeb3Provider="https://mainnet.infura.io/YOUR_API_KEY"
        loading="Loading..."
    >
        <App />
    </Web3Provider>
)

Then in component where you want to use Web3:

import { withWeb3 } from 'react-web3-provider';

class MyComponent {
    render() {
        const { web3 } = this.props;

        web3.eth.getAccounts(console.log);

        // Version 1.0.0-beta.35
        return "Web3 version: {web3.version}";
    }
}

export default withWeb3(MyComponent);