JS Practice — Built-in Objects

Interface — Function as Argument

📖 Usage Example

interface Predicate<T> { (x: T): boolean }
function keepIf<T>(arr: T[], pred: Predicate<T>): T[] {
  return arr.filter(pred)
}

Passing a typed function interface as an argument enforces the callback signature at compile time.

Function Types in Signatures

Challenge: Implement applyCallback<T, U>(value, callback) that applies callback to value and returns the result.

applyCallback(5, x => x * 2)            // → 10
applyCallback('hello', s => s.length)  // → 5

💡 Hints (1)