# TypeScript Best Practices for Large Applications
TypeScript has become the go-to choice for building large-scale JavaScript applications. This guide covers essential patterns and practices for maximizing TypeScript's benefits in complex projects.
## Project Structure and Configuration
### Strict Configuration
Enable strict mode and all strict flags in your tsconfig.json for maximum type safety.
### Path Mapping
Use path mapping to create clean import statements and avoid relative path hell.
### Project References
For large codebases, use project references to improve build performance and enable better code organization.
## Type Design Patterns
### Interface Segregation
Create small, focused interfaces rather than large, monolithic ones.
### Union Types and Discriminated Unions
Use union types for flexibility and discriminated unions for type-safe state management.
### Generic Constraints
Use generic constraints to create reusable, type-safe utilities.
### Utility Types
Leverage built-in utility types like Partial, Pick, Omit, and Record.
## Code Organization
### Barrel Exports
Use index files to create clean public APIs for your modules.
### Type-Only Imports
Use type-only imports to avoid unnecessary runtime dependencies.
### Declaration Merging
Understand when and how to use declaration merging for extending types.
## Error Handling
### Result Types
Implement Result or Either types for explicit error handling.
### Type Guards
Use type guards to safely narrow types and handle edge cases.
### Custom Error Types
Create custom error types with proper type information.
## Performance Considerations
### Avoid Any
Resist the temptation to use 'any' - it defeats the purpose of TypeScript.
### Lazy Loading Types
Use dynamic imports for large type definitions that aren't always needed.
### Build Optimization
Configure your build process to take advantage of TypeScript's incremental compilation.
## Testing with TypeScript
### Type Testing
Write tests for your types using tools like tsd or @typescript-eslint/utils.
### Mock Typing
Properly type your mocks and test doubles.
### Test Utilities
Create typed test utilities for common testing patterns.
## Conclusion
TypeScript's power lies in its ability to provide static typing while maintaining JavaScript's flexibility. By following these best practices, you can build maintainable, scalable applications that leverage TypeScript's full potential.
Remember that TypeScript is a tool to help you write better JavaScript - use it to enhance your development experience, not to over-engineer simple solutions.