code: function NumberToStringJS(radix) {
    // NOTE: Both Number objects and values can enter here as
    // 'this'. This is not as dictated by ECMA-262.
    var number = this;
    if (!IS_NUMBER(this)) {
      if (!IS_NUMBER_WRAPPER(this)) {
        throw MakeTypeError(kNotGeneric, 'Number.prototype.toString');
      }
      // Get the value of this number in case it's an object.
      number = %_ValueOf(this);
    }
    // Fast case: Convert number in radix 10.
    if (IS_UNDEFINED(radix) || radix === 10) {
      return %_NumberToString(number);
    }
  
    // Convert the radix to an integer and check the range.
    radix = TO_INTEGER(radix);
    if (radix < 2 || radix > 36) throw MakeRangeError(kToRadixFormatRange);
    // Convert the number to a string in the given radix.
    return %NumberToRadixString(number, radix);
  }
docs: ---------------------------------------------------------------------------- Number ES6 Number.prototype.toString([ radix ])