typescript-strict

Enable strict mode in your tsconfig.json to activate strict null checks, no implicit any, and other type-safety rules. This enforces compile-time checking for null values, requires explicit type annotations, and prevents unsafe type coercion, catching errors before runtime.

Discriminated unions use a literal type field to distinguish between union members, enabling precise type narrowing. For AST nodes, they ensure the correct properties exist on each node type, eliminating unsafe property access and making type guards predictable.

Define generic constraints using the `extends` keyword to limit what types can be passed. Strict mode requires explicit type parameters and catches mismatches at compile time, ensuring reusable code maintains type safety across different input types.

Type guards narrow types within code blocks using predicates or typeof checks, while null checks verify non-null values. Strict mode requires both: null checks prevent accessing properties on potentially null values, and type guards refine unions to access type-specific properties safely.

Yes, TypeScript generates declaration files automatically when configured. Strict mode ensures inferred types are explicit and accurate, making declaration files reliable for consumers and preventing implicit any leaks in public APIs.

Enabling strict mode on existing code typically requires fixes: adding null checks, explicit type annotations, and type guards. Gradual adoption is possible per-file, but strict mode catches real bugs and prevents entire categories of runtime errors.