JS Practice — Built-in Objects

Symbol.hasInstance — custom instanceof

📖 Usage Example

class EvenNumber {
  static [Symbol.hasInstance](n: unknown) {
    return typeof n === 'number' && n % 2 === 0
  }
}
2 instanceof EvenNumber   // → true

Define static [Symbol.hasInstance] on a class to override how instanceof checks membership.

Custom instanceof with Symbol.hasInstance

A class can define static [Symbol.hasInstance](instance) to customise instanceof.

Challenge: Create a class where all arrays are "instances".

💡 Hints (1)

• Define a static [Symbol.hasInstance] method on your class.