Don't use Babel transpilers when debugging an application

Babel is an essential tool in modern JavaScript development, allowing us to use the latest ECMAScript features while maintaining compatibility with older environments. However, when it comes to debugging, Babel's transpilation can create significant obstacles.

The Problem with Transpiled Code

When you debug transpiled code, you're not actually debugging your source code. You're debugging the transformed output. This creates several issues:

Line Numbers Don't Match

Even with source maps, the debugging experience is suboptimal. Stack traces point to transpiled code, and setting breakpoints can be unpredictable.

Transformed Logic

Babel transforms your code in ways that can obscure the original logic:

• Async/await gets transformed into complex generator functions
• Class syntax becomes constructor functions and prototypes
• Arrow functions are converted to regular functions
• Destructuring is expanded into verbose assignments

Performance Impact

Running Babel during development adds overhead. Every file change requires retranspilation before you can test your code.

Better Debugging Strategies

Use Node.js Native Features

Modern Node.js versions support most ES6+ features natively:

• Async/await
• Arrow functions
• Template literals
• Destructuring
• Classes
• Let and const

For Node.js applications, you often don't need Babel at all during development.

Conditional Transpilation

Structure your project to:

• Run native code in development
• Transpile only for production or when targeting older environments
• Use different entry points for development vs production

Example package.json:

{
  "scripts": {
    "dev": "node src/index.js",
    "build": "babel src --out-dir dist",
    "start": "node dist/index.js"
  }
}

Use Modern Node.js

Keep Node.js updated. Each new version adds support for more JavaScript features, reducing your need for transpilation.

Debug Production Issues Differently

For production debugging:

• Ensure source maps are properly configured and deployed
• Use APM tools that understand source maps
• Reproduce issues in development when possible

When Babel is Necessary

There are legitimate cases where you need Babel during development:

• Experimenting with stage-3 or stage-4 proposals
• Using JSX (React)
• Targeting multiple environments simultaneously
• Testing specific transpilation behaviors

In these cases, invest in proper source map configuration and debugging tools that work well with transpiled code.

Conclusion

Babel is a powerful tool, but it shouldn't run by default during development if you don't need it. By leveraging modern Node.js features and reserving transpilation for production builds, you can significantly improve your debugging experience and development velocity.

The best code to debug is code that hasn't been transformed. Whenever possible, run your source code directly.