JS Practice — Built-in Objects

Generics — getLength<T extends {length}>

📖 Usage Example

function getLength<T extends { length: number }>(x: T): number { return x.length }
getLength([1, 2, 3])   // → 3
getLength('hello')     // → 5

A generic constraint T extends { length: number } allows the function to work on any 'lengthable'.

Generic Constraints

T extends { length: number } is a constraint — it allows any type that has a length property (arrays, strings, etc.).

Challenge: Implement getLength<T extends { length: number }>(x: T): number.

getLength([1, 2, 3])  // → 3
getLength('hello')   // → 5

💡 Hints (1)

• The constraint T extends { length: number } ensures .length is always available.