How to fix Node cannot find module “fs” when using Webpack?

To fix Node cannot find module "fs" when using Webpack, we set target to 'node'.

For instance, in webpack.config.js, we write

module.exports = {
  entry: "./app",
  output: {
    path: __dirname,
    filename: "bundle.js",
  },
  module: {
    loaders: [
      {
        test: /\.js$/,
        exclude: "node_modules",
        loader: "babel",
        query: { presets: ["es2015"] },
      },
    ],
  },
  target: "node",
};

to set target to 'node' to make Webpack build for Node.js instead of browser.