Legacy Code Modernization Skill

I have analyzed the Node.js v10 Express application. The primary risks involve the transition from callback-based error handling to async/await and the replacement of the deprecated Request library with Axios, which handles streams and errors differently.

Legacy Modernization Plan

Legacy Inventory

Modernization Roadmap

Phase 1 — Characterization & Tooling

• Scope: Establish baseline behavior for all Request-based service calls.
• Tasks: Implement nock for HTTP mocking and add Jest snapshot tests for current API responses.
• Exit Criteria: 80% coverage of core business logic paths.

Phase 2 — Runtime & Dependency Preparation

• Scope: Update package.json and engine requirements.
• Tasks: Upgrade Node in CI; install Axios; keep Request as a peer dependency during transition.
• Exit Criteria: Build passes on Node 20 with existing callback code.

Phase 3 — Incremental Refactor
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Scope: Convert middleware and routes to async functions; wrap Request calls in a Promise wrapper before full Axios replacement.

• Tasks: Replace (err, res) => ... with try/catch blocks. Implement Axios adapter.
• Verification: Run snapshot tests after every 5 converted routes.

Risk Register

Next steps

1. Run npm list and share the full output to identify transitive dependency conflicts.
2. Provide the main app.js or entry point to define the Global Error Handler strategy.
3. Identify the most critical API endpoint to serve as the Pilot migration.