TypeScript Tooling Migration

Guide for migrating or upgrading TypeScript tooling in the Phoenix monorepo. This skill covers upgrading core dependencies (TypeScript, React), switching tools (linters, formatters, bundlers), and managing breaking changes across js/app/ and js/ directories.

Monorepo Structure

All TypeScript code lives in a single pnpm workspace rooted at js/:

Shared Dependencies

Shared tooling versions are managed at the workspace root where possible:

Config File Locations

Migration Types

Type 1: Tool Replacement (e.g., ESLint → oxlint)

Complete replacement of one tool with another.

Workflow:

1. Research new tool's migration guide
2. Install new tool alongside old
3. Create new config, verify it works
4. Update package scripts
5. Update pre-commit hooks
6. Remove old tool and config
7. Update documentation

Type 2: Major Version Upgrade (e.g., TypeScript 5 → 6)

Upgrading a tool to a new major version with breaking changes.

Workflow:

1. Read changelog/migration guide for breaking changes
2. Check compatibility of dependent packages
3. Upgrade in a branch, fix breaking changes
4. Run full test suite
5. Update any deprecated config options
6. Update documentation if APIs changed

Type 3: Dependency Upgrade (e.g., React 18 → 19)

Upgrading a core dependency that affects application code.

Workflow:

1. Check compatibility matrix (React + React DOM + types)
2. Review breaking changes and new features
3. Upgrade dependencies together
4. Fix breaking changes in application code
5. Update any deprecated patterns
6. Run E2E tests to verify functionality

Migration Workflow

Phase 1: Research and Planning

1. Read official migration guides - Most tools publish upgrade guides
2. Check GitHub issues - Look for known migration problems
3. Identify scope:
   • Which directories affected (js/app/, js/, or both)
   • What config files need changes
   • What dependencies to add/remove/upgrade
   • What code changes are required
4. Review current configs - Understand existing setup before changing
5. Check dependent packages - Ensure compatibility across the dependency tree

Phase 2: Create a Migration Branch

git checkout -b chore/migrate-<tool>-to-<version>
# or
git checkout -b chore/upgrade-<tool>-<version>

Phase 3: Install/Upgrade Dependencies

# For js/app/ (the app workspace package)
cd js/app && pnpm add -D <package>@<version>

# For js/ (workspace root)
cd js && pnpm add -D -w <package>@<version>

# For upgrading existing dependencies
cd js/app && pnpm update <package>@<version>

Tip: Keep old tool installed until migration is verified for tool replacements.

Phase 4: Update Configuration

For tool replacements - create new config:

Phoenix uses nested configs with inheritance where possible:

phoenix/
├── .<tool>rc.json           # Shared base config
├── js/app/
│   └── .<tool>rc.json       # Extends base, adds React-specific options
└── js/
    └── .<tool>rc.json       # Extends base, adds Node-specific options

Config inheritance pattern:

{
  "$schema": "./node_modules/<tool>/configuration_schema.json",
  "extends": ["../.<tool>rc.json"]
}

For version upgrades - update existing config:

1. Check for deprecated options in the changelog
2. Update or remove deprecated settings
3. Add any new required settings

Phase 5: Fix Breaking Changes

Code changes:

• Fix type errors from stricter checks
• Update deprecated API usage
• Adapt to new syntax requirements

Config changes:

• Update deprecated config options
• Adjust for changed defaults

Tip: Use the tool's own CLI to identify issues:

pnpm run typecheck  # TypeScript errors
pnpm run lint       # Linter errors
pnpm run build      # Build errors

Phase 6: Update Package Scripts

Update both js/app/package.json and js/package.json if script invocations changed:

{
  "scripts": {
    "lint": "<new-command>",
    "typecheck": "<new-command>"
  }
}

Phase 7: Update Pre-commit Hooks

Edit .pre-commit-config.yaml if the tool is used in pre-commit:

1. Remove old tool's hook (for replacements)
2. Update or add new hook:

- id: <tool>-app
  name: <tool> (app)
  entry: pnpm --dir js/app run <script>
  language: system
  files: ^js/app/.*\.[jt]sx?$
  pass_filenames: false
- id: <tool>-js
  name: <tool> (js)
  entry: pnpm --dir js run <script>
  language: system
  files: ^js/.*\.[jt]sx?$
  pass_filenames: false

Phase 8: Update Editor Settings

1. Update .vscode/extensions.json if extensions changed
2. Document any path/binary settings in DEVELOPMENT.md:

{
  "<extension>.path.<binary>": "js/app/node_modules/<package>/bin/<binary>"
}

Note: .vscode/settings.json is gitignored - document settings in DEVELOPMENT.md.

Phase 9: Remove Old Tool (for replacements)

# Remove old dependencies
cd js/app && pnpm remove <old-tool> <old-plugins>
cd js && pnpm remove -w <old-tool> <old-plugins>

# Delete old config files
rm js/app/<old-config> js/<old-config>

Phase 10: Test and Verify

# Type checking
cd js/app && pnpm run typecheck
cd js && pnpm run typecheck

# Linting
cd js/app && pnpm run lint
cd js && pnpm run lint

# Formatting
cd js/app && pnpm run fmt:check
cd js && pnpm run fmt:check

# Unit tests
cd js/app && pnpm test
cd js && pnpm run -r test

# Build
cd js/app && pnpm run build
cd js && pnpm run -r build

# E2E tests (for significant changes)
cd js/app && pnpm run test:e2e

# Pre-commit hooks
pre-commit run --all-files

Phase 11: Update Documentation

Files to check and update:

Phase 12: Keep Shared Tool Versions Aligned

The app (js/app/package.json) and the workspace root (js/package.json) both declare shared tooling (typescript, oxlint, oxfmt). Keep those versions aligned when upgrading — the single lockfile makes drift visible in review.

Key Principles

Keep Packages in Sync

When upgrading shared tooling, upgrade js/app/ and the js/ workspace root together. Version drift causes subtle bugs and CI failures.

Performance Matters

• Measure before/after for build times, lint times, test times
• Some compatibility layers (like JS plugins for linters) add significant overhead
• Prefer native implementations over compatibility shims

Backwards Compatibility

• Many tools support legacy config formats (e.g., oxlint supports eslint-disable comments)
• Don't mass-update working code unless there's a clear benefit
• Deprecation warnings are informational - fix them but don't block on them

Config Location Strategy

Out of Scope Directories

These directories have their own tooling and should NOT be included in migrations:

• scripts/docker/devops/oidc-server/ - Separate OIDC test server
• scripts/mock-llm-server/ - Separate mock server
• internal_docs/ - Internal documentation utilities

Troubleshooting

TypeScript Upgrade Issues

Stricter type checking: New TypeScript versions often add stricter checks. Fix errors by:

1. Adding explicit type annotations
2. Using type assertions where appropriate
3. Updating tsconfig.json to temporarily relax checks if needed

Dependency type mismatches: Ensure @types/* packages are compatible with the new TS version.

Build Failures After Upgrade

1. Clear caches: rm -rf node_modules/.cache js/app/dist js/**/dist
2. Reinstall: pnpm install
3. Rebuild: pnpm run build

Config Not Found

• Check $schema path is relative to the config file location
• For nested configs, verify extends path (e.g., "../.toolrc.json")

Editor Not Using Updated Tool

1. Ensure extension is up to date
2. Set explicit binary path in VS Code settings
3. Reload VS Code window (Cmd+Shift+P → "Reload Window")

Pre-commit Hook Fails

• Run pnpm install in both directories
• Verify script name in package.json matches hook entry
• Test script manually: pnpm --dir js/app run <script>

CI Fails But Local Passes

• Check Node version matches CI (see .nvmrc)
• Ensure lockfile is committed (pnpm-lock.yaml)
• Run with --frozen-lockfile locally to match CI behavior

CI Workflows

Relevant CI files for TypeScript tooling:

References

General

• TypeScript Release Notes
• React Release Notes
• Vite Migration Guide

Current Tools

• Oxlint docs
• Oxfmt docs
• pnpm docs