#Migration

Legacy Code Migration Pipeline

Modernize your codebase one module at a time — overnight.

The Scenario

Your codebase has legacy patterns: class components, callback-based APIs, deprecated dependencies, or outdated conventions. A full migration would take weeks of developer time and risk introducing regressions. You need incremental, safe modernization.

Who Is This For

Teams maintaining codebases older than 2-3 years that have accumulated legacy patterns. Especially useful for React class-to-hooks migrations, Node.js callback-to-async migrations, and framework version upgrades.

Pipeline Steps

01

Identify Legacy Patterns

Claude Code

Agent scans the codebase for legacy patterns you've defined: class components, var declarations, callback patterns, deprecated APIs.

02

Prioritize Migration Tasks

Claude Code

Agent ranks files by migration complexity and dependency count. Leaf nodes (files with no dependents) get migrated first.

03

Migrate Individual Files

Claude Code

Each file is migrated independently: legacy pattern removed, modern pattern applied, imports updated.

04

Verify with Tests + Type Check

Jest + TypeScript

Full test suite and type checker run after each migration. Failed migrations are reverted and flagged.

05

Individual PRs

Git

Each successfully migrated file gets its own PR, making review easy and rollback trivial.

Expected Results

  • 30-60 files migrated per overnight run
  • Individual PRs per file for easy review
  • Zero regressions — all tests pass before PR creation
  • Migration progress report showing before/after pattern counts
Estimated Runtime8-12 hours overnight for 30-60 file migrations

Frequently Asked Questions

Any pattern migration: React class to hooks, callbacks to async/await, CommonJS to ESM, jQuery to vanilla JS, and more. Define your source and target patterns.

Zowl runs a full project type check and test suite after each migration. If anything breaks, the migration is reverted and flagged for manual review.

Yes. Zowl tracks which files have been migrated. Run the pipeline nightly until the full codebase is modernized.

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