Tree shaking doesn't work with babel loader in webpack 4

Question

I'm tinkering with the tree shaking example from the webpack document. But it seems that tree shaking doesn't work once I add babel-loader to the mix. Here is an overview of my project:

index.js:

import { cube } from "./math";

function component() {
  const element = document.createElement('pre');

  element.innerHTML = [
    'Hello webpack!',
    '5 cubed is equal to ' + cube(5)
  ].join('\n\n');

  return element;
}

document.body.appendChild(component());

math.js:

export function square(x) {
  console.log('square');
  return x * x;
}

export function cube(x) {
  console.log('cube');
  return x * x * x;
}

.babelrc:

{
	"presets": [
      ["env", { "modules": false }],
      "react"
    ],
	"plugins": ["react-hot-loader/babel"]
}

package.json:

{
  "dependencies": {
    "react": "^16.3.1",
    "react-dom": "^16.3.1",
    "react-hot-loader": "^4.0.1"
  },
  "name": "react-webpack-starter",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "scripts": {
    "start": "webpack-dev-server --mode development --open --hot",
    "build": "webpack -p --optimize-minimize"
  },
  "sideEffects": false,
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.4",
    "babel-preset-env": "^1.6.1",
    "babel-preset-react": "^6.24.1",
    "html-webpack-plugin": "^3.2.0",
    "webpack": "^4.5.0",
    "webpack-cli": "^2.0.14",
    "webpack-dev-server": "^3.1.3"
  }
}

webpack.config.js:

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
	entry: './src/index.js',
	output: {
		path: path.join(__dirname, '/dist'),
		filename: 'index_bundle.js'
	},
	mode: 'production',
	module: {
		rules: [
			{
				test: /\.js$/,
				exclude: /node_modules/,
				use: {
					loader: 'babel-loader'
				}
			}
		]
	},
	plugins: [
		new HtmlWebpackPlugin({
			template: './src/index.html'
		})
	]
};

As index.js is not consuming the square function, the square function should be pruned out of the bundle. However, when I open up the bundle.js and search for 'square', I can still find the square function and the console log statement. After I comment out the babel-loader specification in webpack config and npm run build again, the "square" word is nowhere to be seen in the generated bundle file.

I did specify modules: false in .babelrc.
Can anyone tell me what could be causing this problem?
Here's the repo for reproduction: https://github.com/blogrocks/treeshaking-issue.git

Answer 1

My problem finally got resolved. I should have specified "cross-env NODE_ENV=production" when running webpack. And it's not even sufficient to use DefinePlugin to set NODE_ENV to "production" in plugins. It seems babel-loader keys off the "NODE_ENV=production" from the command.

Oh, I finally find that it is react-hot-loader that is keying off NODE_ENV=production from the command!!