next.js/examples/with-webpack-bundle-analyzer/next.config.js

const {BundleAnalyzerPlugin} = require('webpack-bundle-analyzer')
module.exports = {
  webpack: (config, { dev }) => {
    // Perform customizations to config
    config.plugins.push(
      new BundleAnalyzerPlugin({
        analyzerMode: 'disabled',
        // For all options see https://github.com/th0r/webpack-bundle-analyzer#as-plugin
        generateStatsFile: true,
        // Will be available at `.next/stats.json`
        statsFilename: 'stats.json'
      })
    )
    // Important: return the modified config
    return config
  }
}