Testing types in TypeScript is crucial for SDK and API developers to ensure predictable type inferences. Tools like `tsc`, `dtslint`, `tsd`, and `Vitest` can help catch errors early and guarantee type behavior.
Node.js EventEmitter can be made type-safe in TypeScript using declaration merging. This ensures correct event names and listener signatures, enhancing IDE and type checker reliability. Additional libraries like "typed-emitter" can further streamline the process.
Private fields in TypeScript can be declared with either "private" or "#". The private keyword only enforces privacy at design time through the TypeScript compiler, while the "#" syntax creates Private Elements that are also protected from outside access at runtime. Private Elements provide stronger encapsulation because their fields remain completely hidden from anything outside the class.
TypeScript 5.3 introduces switch-true narrowing, a feature that simplifies complex if/else chains. By using switch-true narrowing, conditions can be expressed more declaratively, improving code readability and type safety.
Async generators in TypeScript can simplify handling user input in CLI tools. They yield values over time, making code cleaner and easier to follow. This approach can also be applied to various sources beyond CLI input.