Troubleshooting Webpack ES6+ Transpilation Issues

If Webpack isn’t correctly transpiling your ES6+ code to browser-compatible JavaScript, here are the key areas to check:

Common Causes and Solutions

1. Missing or Misconfigured Babel

npm install --save-dev @babel/core @babel/preset-env babel-loader

webpack.config.js:

module: {
  rules: [
    {
      test: /\.js$/,
      exclude: /node_modules/,
      use: {
        loader: 'babel-loader',
        options: {
          presets: ['@babel/preset-env']
        }
      }
    }
  ]
}

2. Missing .babelrc Configuration

Create .babelrc or babel.config.js:

{
  "presets": [
    ["@babel/preset-env", {
      "targets": "> 0.25%, not dead",
      "useBuiltIns": "usage",
      "corejs": 3
    }]
  ]
}

3. Check Webpack Mode

Ensure you’re not in production mode if you want to see non-minified output:

module.exports = {
  mode: 'development', // or 'production'
  // ...
}

4. Source Maps Configuration

Add source maps for better debugging:

devtool: 'source-map',

5. Polyfill Configuration (for missing features)

Install core-js:

npm install core-js regenerator-runtime

Then at your entry point:

import 'core-js/stable';
import 'regenerator-runtime/runtime';

Verification Steps

Check your output bundle:

Look for ES6 syntax that shouldn’t be there
Search for => (arrow functions) or class to verify transpilation

Run:

npx webpack --stats verbose

to get detailed build information

Check browser support targets in your Babel configuration match your requirements

Advanced Configuration

For more complex setups, consider adding these plugins:

npm install --save-dev @babel/plugin-transform-runtime @babel/runtime

Update your Babel config:

{
  "plugins": [
    ["@babel/plugin-transform-runtime", {
      "corejs": 3
    }]
  ]
}

If you’re still having issues, please share:

Your webpack version (webpack -v)
Your babel version (npx babel --version)
Relevant parts of your webpack.config.js and package.json
The specific ES6+ features that aren’t being transpiled

Webpack not transpiling ES6+ correctly