Webpack tree shaking still bundles unused exports

Question

I am trying to test out Webpack's tree shaking feature, but it does not appear to be working.

Here are my files:

• index.ts

import { good } from './exports';
console.log(good);

• exports.ts

export const good = 'good';
export const secret = 'iamasecret';

• tsconfig.json

{}

• webpack.config.ts

import { Configuration } from 'webpack';
import  * as TerserPlugin from "terser-webpack-plugin";
const config: Configuration = {
    mode: 'production',
    entry: './index.ts',
    module: {
        rules: [
          {
            test: /\.tsx?$/,
            use: 'ts-loader',
            exclude: /node_modules/,
          },
        ],
      },
      resolve: {
        extensions: [ '.tsx', '.ts', '.js' ]
      },
      optimization: {
        usedExports: true,
        minimizer: [new TerserPlugin()],
      }
}
export default config;

• package.json

{
  "name": "webpacktest",
  "version": "1.0.0",
  "description": "",
  "main": "index.ts",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@types/terser-webpack-plugin": "^2.2.0",
    "@types/webpack": "^4.41.11",
    "terser-webpack-plugin": "^2.3.5",
    "ts-loader": "^7.0.0",
    "ts-node": "^8.8.2",
    "typescript": "^3.8.3",
    "webpack": "^4.42.1",
    "webpack-cli": "^3.3.11"
  },
  "sideEffects": false
}

When I run npx webpack it bundles the files into dist/main.js. When I open that file, the secret string is in there despite it being an unused export. Is there a way that I can stop it from being included in the final bundle?

Answer 1

Ok, so I figured it out. I needed to install the packages @babel/core, @babel/preset-env, and babel-loader as dev-dependencies, and change my Webpack config rule for handling TypeScript files to:

    {
        test: /\.tsx?$/,
        use: ['babel-loader','ts-loader'],
        exclude: /node_modules/,
    },

Next, I created a .babelrc file with the following content:

{
    "presets": [
        [
            "@babel/preset-env",
            {
                "modules": false
            }
        ]
    ]
}

Finally, I changed/added the following lines to my tsconfig.json under compilerOptions:

"module": "es6",
"moduleResolution": "node",

Using babel-loader, setting the .babelrc config, and using "module": "es6", allowed for my TypeScript code to be tree-shaken. "moduleResolution": "node" fixed an issue where I was getting errors that certain modules could not be resolved.