JavaScript Demo: Symbol.species

class Array1 extends Array {
  static get [Symbol.species]() { return Array; }
}

const a = new Array1(1, 2, 3);
const mapped = a.map(x => x * x);

console.log(mapped instanceof Array1);
// expected output: false

console.log(mapped instanceof Array);
// expected output: true

JavaScript Demo: Symbol.species

​x
class Array1 extends Array {
  static get [Symbol.species]() { return Array; }
}
​
const a = new Array1(1, 2, 3);
const mapped = a.map(x => x * x);
​
console.log(mapped instanceof Array1);
// expected output: false
​
console.log(mapped instanceof Array);
// expected output: true
​