From 66 TypeScript Errors to Production: A Full-Stack Debugging Journey

The Challenge

I encountered a critical deployment blocker in my ERP frontend application when attempting to build for production. The TypeScript compiler reported 66 errors, preventing the creation of Docker containers needed for deployment alongside the already-functioning backend. My goal was clear: resolve all TypeScript errors systematically to achieve a successful production build and enable Docker Compose deployment.

Initial Assessment

My first step was understanding the scope and patterns of the errors:

npm run build:prod 2>&1 | grep "error TS" | wc -l
# Output: 66

To identify which files had the most issues, I analyzed the error distribution:

npm run build:prod 2>&1 | grep "error TS" | grep -o "src/[^(]*" | sort | uniq -c | sort -rn

This revealed that test files, particularly hrSlice.test.ts (11 errors) and Dashboard.test.tsx (7 errors), contained the majority of issues.

Core Issues Discovered

1. Missing Redux Store Slices

Discovery Command:

find src/store/slices -name "*.ts" -exec grep -l "interface.*State" {} \;

I discovered that my store configuration only registered 4 slices (auth, production, hr, ui) while the codebase actually contained 7 slices. The missing slices (analytics, experiments, featureFlags) caused components attempting to access them to fail TypeScript validation.

Solution: Updated src/store/index.ts to include all seven slices in the store configuration.

2. Type Definition Drift

Investigation Commands:

grep -A 15 "export interface Employee" src/types/index.ts
grep -A 25 "export interface ProductionOrder" src/types/index.ts

I found that the codebase had evolved with some components expecting properties like status, phone, and startDate while the interfaces defined employmentStatus, phoneNumber, and employmentDate. This revealed a pattern where the codebase had transitioned to more specific property names over time.

Solution: Created type extensions (src/types/typeExtensions.ts) that added backward-compatible properties to interfaces, allowing both old and new property names to coexist during the transition period.

3. Incomplete Mock Redux States in Tests

Pattern Recognition Command:

npm run build:prod 2>&1 | grep -A 2 "missing the following properties"

Test files were creating partial Redux states (e.g., only providing production slice) when TypeScript expected all seven slices to be present. This was like trying to test a component with an incomplete application state.

Solution: Created comprehensive mock data factories (src/test-utils/mockData.ts) that generate complete Redux states with all required slices, while allowing tests to override specific properties:

export const createMockRootState = (overrides?: DeepPartial<RootState>): RootState => {
  // Returns complete state with all 7 slices
  // Supports deep merging for customization
};

4. React Router v6 Pattern Mismatches

Component Structure Analysis:

grep "Outlet\|Navigate" src/components/auth/PrivateRoute.tsx

I discovered that PrivateRoute used React Router v6's <Outlet /> pattern rather than accepting children as props. Tests were written for the older pattern, causing type errors.

Solution: Restructured tests to work with the Outlet pattern by creating proper route hierarchies that mirror the actual application routing structure.

5. Missing Dependencies

Dependency Check:

grep "react-beautiful-dnd" package.json

The ProductionScheduling component imported react-beautiful-dnd for drag-and-drop functionality, but the package wasn't installed, causing import errors.

Solution:

npm install react-beautiful-dnd@13.1.1 @types/react-beautiful-dnd@13.1.4 --save

Resolution Progress

The debugging process followed a systematic pattern of identifying root causes and applying targeted fixes:

• 66 → 47 errors: Connected missing Redux slices
• 47 → 40 errors: Fixed type extensions and added missing properties
• 40 → 34 errors: Updated production slice to use extended types
• 34 → 27 errors: Fixed Dashboard test with complete mock states
• 27 → 16 errors: Corrected hrSlice test store configuration
• 16 → 5 errors: Fixed remaining test mock data issues
• 5 → 0 errors: Added parameter support to mock state factories

Key Technical Insights

Type System as Documentation

TypeScript errors revealed the evolution of my codebase. Property name changes from generic (status) to specific (employmentStatus) showed intentional improvements in domain modeling. The type system acted as living documentation of these architectural decisions.

Test Infrastructure Must Mirror Production

My most significant learning was that test mock data must match production interfaces exactly, even when testing isolated functionality. Creating comprehensive mock utilities that provide complete, valid states while supporting customization proved essential for maintainable tests.

Deep Merge Pattern for Test Data

Implementing deep merge functionality for mock state creation allowed tests to specify only the properties they care about while maintaining complete type safety:

const preloadedState = createMockRootState({
  production: { ordersLoading: true }
  // All other slices and properties use defaults
});

Evolution Patterns in Large Codebases

I observed how codebases naturally evolve with multiple patterns coexisting. Modern React Router v6 Outlet patterns lived alongside older routing approaches. Newer TypeScript interfaces coexisted with code expecting older property names. Understanding these evolution patterns was crucial for creating backward-compatible solutions.

Final Build Success

After resolving all 66 TypeScript errors, the production build succeeded:

npm run build:prod
# ✓ 14138 modules transformed
# ✓ built in 43.99s

The application successfully compiled into optimized bundles totaling approximately 3.5 MB (486 KB gzipped for the main bundle), ready for Docker containerization and deployment.

Technical Accomplishments

Through this debugging journey, I:

• Diagnosed and resolved 66 TypeScript errors across 14 different source files
• Created reusable mock data utilities supporting 7 Redux slices with deep partial overrides
• Implemented backward-compatible type extensions to support codebase evolution
• Harmonized testing patterns across component and slice tests
• Established consistent type contracts from Redux store through React components

Deployment Readiness

With the successful build, my frontend application now produces static assets in the build/ directory, ready for containerization with Docker and deployment via Docker Compose alongside the backend services. The systematic approach to resolving these errors not only unblocked deployment but significantly improved code quality and maintainability.

Reflection

This debugging experience reinforced the value of systematic problem-solving in complex TypeScript applications. Rather than patching individual errors, I focused on understanding root causes and creating comprehensive solutions. The investment in proper type definitions and test infrastructure will accelerate future development and reduce runtime errors.

The journey from 66 errors to zero taught me that TypeScript's strictness, while sometimes challenging during development, provides invaluable safety guarantees for production applications. Each error fixed was a potential runtime bug prevented, making the application more robust and reliable for end users.

If you enjoyed this article, you can also find it published on LinkedIn and Medium.