I believe you can do this with `Reflect.construct`.

```js
function SubArray(arg1) {
  return Reflect.construct(Array, arguments, SubArray);
}
SubArray.prototype = Object.create(Array.prototype);
Reflect.setPrototypeOf(SubArray, Array);

var arr = new SubArray();
arr instanceof SubArray; // true
arr instanceof Array; // true
arr[5] = 0; // should exotically update length property
arr.length === 6; // true
```
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I believe you can do this with `Reflect.construct`.

```js
function SubArray(arg1) {
  return Reflect.construct(Array, arguments, new.target);
}
SubArray.prototype = Object.create(Array.prototype);
Reflect.setPrototypeOf(SubArray, Array);

var arr = new SubArray();
arr instanceof SubArray; // true
arr instanceof Array; // true
arr[5] = 0; // should exotically update length property
arr.length === 6; // true
```

edit: fixed an issue mentioned below