Question 1

How do I create generic functions with constraints in TypeScript?

Accepted Answer

Generic functions use type parameters like to stay flexible while preserving types. Add constraints with extends, such as , so only types meeting the constraint are accepted while inference still works automatically.

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. Applying it to typeof your function yields the exact return type at compile time.

Question 3

What is the difference between mapped types and conditional types?

Accepted Answer

Mapped types iterate over an existing type's keys to transform properties, like making them readonly or optional. Conditional types select a type based on a check, such as T extends string ? A : B, enabling type-level logic.

Question 4

Does TypeScript support type-safe event emitters?

Accepted Answer

Yes, by defining an event map interface and using generics with keyof, the emitter enforces correct event names and payload types at compile time. Mismatched payloads produce type errors before runtime.

Question 5

When should I avoid complex conditional types in TypeScript?

Accepted Answer

Avoid deeply nested or recursive conditional types when they slow compilation or hurt readability. Prefer simpler type compositions, cache computed types, and limit recursion depth to keep build times reasonable.

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