Modernizing Legacies: Refactoring Monoliths with AI

The JS/TS Modernizer

Upgrading from ES5 (vars, callbacks) to modern TypeScript is tedious. Copilot acts as an automated translation layer, handling the syntax drudgery so you can focus on the logic.

From Callbacks to Async/Await

// Old: Callback Hell
function getUser(id, callback) {
  db.query('SELECT * FROM users WHERE id = ?', [id], function(err, user) {
     if (err) return callback(err);
     callback(null, user);
  });
}

Prompt: "Refactor this to use async/await and TypeScript types."

// New: Clean Async TypeScript
async function getUser(id: string): Promise {
  const user = await db.query('SELECT * FROM users WHERE id = ?', [id]);
  return user;
}

Breaking the Monolith

Extracting microservices starts with untangling domain logic. You can highlight a chunk of a massive controller file and ask Copilot to "Extract the billing logic into a separate service class."

Modular Extraction

Instead of manually copy-pasting and fixing imports, let Copilot move the code. It often correctly identifies the necessary dependencies to import in the new file, saving you from "ReferenceError" hell.

Tech Debt Downpayment

The scariest part of refactoring is the lack of tests. "I don't know what this does, and I'm afraid to break it."

Test Before You Touch

Strategy: highlight the legacy function and ask Copilot: "Write a unit test that covers the main success and failure paths for this function."

Once you have a passing test suite for the old code, you can refactor with confidence, knowing you'll be alerted immediately if you break existing behavior.

Conclusion

Modernization is no longer a choice between a complete rewrite or stagnation. With AI-assisted refactoring, you can chip away at your monolith, progressively improving code quality and migrating to modern standards without bringing business to a halt.