TypeScript Best Practices for Large-Scale Applications

TypeScript has become the standard for building large-scale JavaScript applications. Here are the practices that help codebases remain maintainable as they grow.

Strict Mode is Non-Negotiable

Enable strict mode from day one. The short-term friction pays off enormously in catching bugs early and making refactoring safer.

Discriminated Unions Over Optional Properties

Model your domain with discriminated unions rather than objects with many optional properties. This approach makes invalid states unrepresentable.

Branded Types for Domain Modeling

Use branded types to distinguish between values that have the same underlying type but different semantic meanings. A UserId and a ProductId should not be interchangeable even if both are strings.

Dependency Injection

Structure your code for testability with dependency injection. This makes unit testing straightforward and allows for easy mocking of external services.

Error Handling Patterns

Adopt consistent error handling patterns. Consider using Result types or discriminated unions for operations that can fail predictably.

Code Organization

• Organize by feature, not by type
• Keep modules small and focused
• Export only what is needed
• Use barrel files judiciously