DEV Community

DevToolPad_Creator
DevToolPad_Creator

Posted on

I built a JavaScript TypeScript converter after struggling with manual migration

#javascript #showdev #tooling #typescript

After working with JavaScript for years, moving to TypeScript felt like the obvious next step—better tooling, safer code, and fewer runtime surprises.

But when I actually tried converting real-world JavaScript code to TypeScript… it wasn’t as smooth as I expected.

This post is based on what I learned while doing that migration—and why I ended up building a small tool to make the process easier.

🚧 The Reality of Converting JavaScript to TypeScript

At first, I thought:

“Just rename .js to .ts and fix errors.”

In reality, the challenges were:

  • Implicit any everywhere
  • Dynamic objects with unpredictable shapes
  • Utility functions with flexible arguments
  • Lack of clear interfaces

🧪 Example 1: Simple Function Conversion

JavaScript 

function add(a, b) {
  return a + b;
}
Enter fullscreen mode Exit fullscreen mode

TypeScript (Expected) 

function add(a: number, b: number): number {
  return a + b;
}
Enter fullscreen mode Exit fullscreen mode

👉 Easy… until your inputs are not always numbers.

🧪 Example 2: Real Problem — Dynamic Object

JavaScript 

function printUser(user) {
  console.log(user.name);
}
Enter fullscreen mode Exit fullscreen mode

TypeScript (Naive Conversion) 

function printUser(user: any) {
  console.log(user.name);
}
Enter fullscreen mode Exit fullscreen mode

👉 This works, but defeats the purpose of TypeScript.

Better Version 

type User = {
  name: string;
};

function printUser(user: User) {
  console.log(user.name);
}
Enter fullscreen mode Exit fullscreen mode

⚠️ Where Things Get Messy

The hardest parts during migration:

  • Large files with mixed logic
  • API responses with unknown structure
  • Reusable helpers used across the app
  • Optional / nullable fields

👉 These are NOT solved automatically—you still need manual thinking.

🛠️ Why I Built a Small Tool

While working through this, I noticed:

  • I was repeatedly converting similar patterns
  • Writing boilerplate types again and again
  • Doing small “first-step” conversions manually

So I built a simple tool to:

  • Quickly convert basic JS structures into TS
  • Give a starting point (not a final solution)
  • Save time during early migration

👉 You can try it here:
https://devtoolpad.com/javascript-to-typescript

💡 Important: Tools Won’t Replace Thinking

Even with automation, you still need to:

  • Design proper types
  • Handle edge cases
  • Refactor messy logic

👉 Think of tools as:

“A starting point, not a complete migration solution”

🚀 My Recommended Approach

If you're migrating a real project:

  1. Enable TypeScript gradually
  2. Start with smaller modules
  3. Avoid using any unless necessary
  4. Define shared types early
  5. Refactor as you convert

🤔 Final Thought

Switching to TypeScript is 100% worth it—but the migration phase is where most friction happens.

If you’ve gone through this, I’d love to know:
👉 What was the hardest part for you while converting JS to TS?

Let’s discuss 👇

Top comments (0)