create-react-app (≥ v5.0)

If you are using create-react-app version >=5 you may run into issues building. This is because NodeJS polyfills are not included in the latest version of create-react-app.

Reference: https://github.com/web3/web3.js#web3-and-create-react-app

The solution is to install react-app-rewired and the missing modules.

If you are using yarn:

yarn add --dev react-app-rewired process crypto-browserify stream-browserify assert stream-http https-browserify os-browserify url buffer

If you are using npm:

npm install --save-dev react-app-rewired crypto-browserify stream-browserify assert stream-http https-browserify os-browserify url buffer process

Create config-overrides.js in the root of your project folder with the content:

const webpack = require('webpack');

module.exports = function override(config) {
    const fallback = config.resolve.fallback || {};
    Object.assign(fallback, {
        "crypto": require.resolve("crypto-browserify"),
        "stream": require.resolve("stream-browserify"),
        "assert": require.resolve("assert"),
        "http": require.resolve("stream-http"),
        "https": require.resolve("https-browserify"),
        "os": require.resolve("os-browserify"),
        "url": require.resolve("url")
    })
    config.resolve.fallback = fallback;
    config.plugins = (config.plugins || []).concat([
        new webpack.ProvidePlugin({
            process: 'process/browser',
            Buffer: ['buffer', 'Buffer']
        })
    ])
    return config;
}

Within package.json change the scripts field for start, build and test. Instead of react-scripts replace it with react-app-rewired