Generics with keyof Constraints

Snippet

Generics with keyof Constraints

Using 'keyof' with generics ensures that a function parameter is a valid key of a specific object, providing full type safety and IDE autocompletion.

snippet.ts
typescript
function getProperty<T, K extends keyof T>(obj: T, key: K) {
  return obj[key];
}
 
const user = { id: 1, name: "Bob" };
const userName = getProperty(user, "name");

Breakdown

K extends keyof T

Constraints the generic type K to only be keys that exist on type T.

obj[key]

TypeScript knows exactly what type the returned value will be based on the key used.

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Generics with keyof Constraints

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