Question 1

How do I use generics with constraints in TypeScript?

Accepted Answer

Use the extends keyword on a type parameter to constrain generics, such as function logLength<T extends HasLength>(item: T). This ensures the argument has the required properties while preserving the specific type passed in.

Question 2

How to create a type-safe event emitter in TypeScript?

Accepted Answer

Define an event map interface mapping event names to payload types, then use generic methods constrained by keyof the map. The on and emit methods infer the correct payload type from the event name automatically.

Question 3

What is the difference between conditional types and mapped types?

Accepted Answer

Conditional types select a type based on a condition using T extends U ? X : Y, while mapped types iterate over an object's keys to transform each property. They are often combined for filtering or remapping object shapes.

Question 4

When should I use type guards instead of type assertions?

Accepted Answer

Use type guards with the value is Type syntax when narrowing unknown or union types at runtime, since they perform actual checks. Type assertions with as bypass compiler verification and can hide runtime errors.

Question 5

What are the limitations of deeply recursive TypeScript types?

Accepted Answer

Deeply nested conditional or recursive types can slow compilation and hit recursion depth limits. Cache complex type computations, limit recursion depth, and prefer simpler types when the extra precision is unnecessary.

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