Child class extending BN, using BN in constructor

[amaury1093]

import BN from "bn.js";

class MyBN extends BN {
  doSomething() {
    console.log("HELLO");
  }
}

const a = new MyBN(new BN(123));
console.log(a.toString());  // this works, logs 123
a.doSomething();

Expected:
Logs HELLO

Actual:
Doesn't log anything on the doSomething line.

Repro:
https://codesandbox.io/s/508mm5zz5l

Notes:
Using typescript 3.0.1

[fanatid]

I think this is expected result, check constructor function:

bn.js/lib/bn.js

Lines 22 to 24 in 24cc2dd

	if (BN.isBN(number)) {
	return number;
	}