Subclassing Javascript Arrays. TypeError: Array.prototype.toString is not generic

Question

Is it possible to subclass and inherit from javascript Arrays?

I\'d like to have my own custom Array object that has all the features of an Array, but contains addit

Answer 1

ES6 minimal runnable example with custom constructor

If you also want to override the constructor, then some extra care is needed because some of the methods will need the old constructor.

Using the techniques mentioned at: How can I extend the Array class and keep its implementations we can reach:

#!/usr/bin/env node

const assert = require('assert');

class MyArray extends Array {
  constructor(nodes, myint) {
    super(...nodes);
    this.myint = myint;
  }

  static get [Symbol.species]() {
    return Object.assign(function (...items) {
      return new MyArray(new Array(...items))
    }, MyArray);
  }

  inc() { return this.myint + 1; }
}

const my_array = new MyArray([2, 3, 5], 9);
assert(my_array[0] === 2);
assert(my_array[1] === 3);
assert(my_array[2] === 5);

assert(my_array.myint === 9);

assert(my_array.inc() === 10);

assert(my_array.toString() === '2,3,5');

my_slice = my_array.slice(1, 2);
assert(my_slice[0] === 3);
assert(my_slice.constructor === MyArray);

Getting the index notation [] without Arrray has been asked at: Implement Array-like behavior in JavaScript without using Array

Tested in Node.js v10.15.1.