Junior (0-2 years)TypeScript
What are generics in TypeScript?
Quick answer
Generics are type parameters: they let a function, class or type work with many types while keeping the relationship between inputs and outputs, instead of falling back to any.
identity<T>(value: T): T returns the same type it received. Without T you would write any and lose that link. Constraints (T extends { id: string }) describe the minimum shape. Several parameters (K, V) model maps and API wrappers.
Common interview follow-ups: default parameters (T = string), keyof T for safe property access, and why Array<T> and T[] are the same. Prefer inference (wrap(user)) over forcing wrap<User>(user) at every call site.
function first<T>(items: T[]): T | undefined {
return items[0];
}
first(["a", "b"]); // string | undefined
first<number>([1, 2, 3]); // number | undefined