JS Practice — Built-in Objects

Array[Symbol.species] — subclass filter()

📖 Usage Example

class MyArr extends Array {}
const a = new MyArr(1, 2, 3, 4)
a.filter(x => x > 2) instanceof MyArr  // → true

filter() on a subclass of Array returns an instance of that subclass via Symbol.species.

Array[Symbol.species] and filter()

Just like .map(), the .filter() method also respects Symbol.species. When called on an Array subclass, it returns an instance of the subclass rather than a plain Array.

Challenge: Create TypedArray that extends Array. Implement filterReturnsSubclass that returns true when .filter() on a TypedArray instance produces another TypedArray instance.

filterReturnsSubclass() // → true

💡 Hints (2)

• `.filter()` uses `Symbol.species` internally to construct its return value.
• Extending `Array` is enough — no need to override `Symbol.species` for the default behaviour.