Question 1

How do I create a type-safe event emitter in TypeScript?

Accepted Answer

Define an event map type mapping event names to payload types, then use generics with `keyof` constraints so `on` and `emit` infer the correct payload type per event. This gives compile-time errors when payloads don't match the registered event shape.

Question 2

How to extract a function's return type in TypeScript?

Accepted Answer

Use a conditional type with `infer`: `type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never`. Passing `typeof myFunction` extracts its return type at compile time without runtime code.

Question 3

What is the difference between mapped types and conditional types in TypeScript?

Accepted Answer

Mapped types iterate over an object's keys to transform properties, like making them optional or readonly. Conditional types select a type based on a check using `extends`, enabling logic like extracting types or distributing over unions.

Question 4

Should I use any or unknown for untyped values in TypeScript?

Accepted Answer

Use `unknown` instead of `any`. `unknown` forces type narrowing through guards or assertions before use, preserving compile-time safety, while `any` disables type checking entirely and can hide runtime errors.

Question 5

When should I avoid deeply nested conditional types in TypeScript?

Accepted Answer

Avoid deep nesting when compilation slows noticeably or types become unreadable. Cache complex type computations in named aliases, limit recursion depth, and prefer simpler type compositions when they achieve the same safety.

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