How do I reduce the bundle size in my Nextjs app

I recommend using this technique for mid-low websites, such as: personal blogs, portfolios, etc. Due to this technique replacing React with Preact might fail in some applications.

1. Install Preact yarn add preact
2. In the next.config.js file add the following code:

module.exports = {
  // ...other config

  webpack: (config, { isServer, dev }) => {
    // Replace React with Preact only in client production build
    if (!dev && !isServer) {
      Object.assign(config.resolve.alias, {
        react: 'preact/compat',
        'react-dom/test-utils': 'preact/test-utils',
        'react-dom': 'preact/compat'
      })
    }

    return config
  }
}

We will replace React with Preact only when building the client on the production side, which of course reduces the bundle size that users have to download by up to 30%!

Good examples on this website:

Before

After