Closure Compiler and "extends"

class ClassA
{
  this.alpha = 3;
}

class ClassB extends ClassA
{
  this.beta = 42;
}


// === after running Closure Compiler becomes

function ClassA()
{
  this.alpha = 3;
}

function ClassB()
{
  ClassA.call(this);
  this.beta = 42;
}

q(ClassB, ClassA); // <<<<<<<<


// === original definition of q() - basically polyfills Object.create and Object.setPrototypeOf
var e = 'function' == typeof Object.create ? Object.create : function(b) {
  function a() {
  }
  a.prototype = b;
  return new a;
}, f;
if ('function' == typeof Object.setPrototypeOf) {
  f = Object.setPrototypeOf;
} else {
  var h;
  a: {
    var k = {s:!0}, m = {};
    try {
      m.__proto__ = k;
      h = m.s;
      break a;
    } catch (b) {
    }
    h = !1;
  }
  f = h ? function(b, a) {
    b.__proto__ = a;
    if (b.__proto__ !== a) {
      throw new TypeError(b + ' is not extensible');
    }
    return b;
  } : null;
}
var n = f;
function q(b, a) {
  b.prototype = e(a.prototype);
  b.prototype.constructor = b;
  if (n) {
    n(b, a);
  } else {
    for (var d in a) {
      if ('prototype' != d) {
        if (Object.defineProperties) {
          var c = Object.getOwnPropertyDescriptor(a, d);
          c && Object.defineProperty(b, d, c);
        } else {
          b[d] = a[d];
        }
      }
    }
  }
  b.F = a.prototype;
}


// === simplified
var e = Object.create, f = Object.setPrototypeOf, n = f;
function q(b, a) {
  b.prototype = e(a.prototype);
  b.prototype.constructor = b;
  if (n) {
    n(b, a);
  } else {
    for (var d in a) {
      if ('prototype' != d) {
        if (Object.defineProperties) {
          var c = Object.getOwnPropertyDescriptor(a, d);
          c && Object.defineProperty(b, d, c);
        } else {
          b[d] = a[d];
        }
      }
    }
  }
  b.F = a.prototype;
}


// === simplified again
var e = Object.create, f = Object.setPrototypeOf, n = f;
function q(b, a) {
  b.prototype = e(a.prototype);
  b.prototype.constructor = b;
  n(b, a);
  b.F = a.prototype;
}


// === and again
function q(b, a) {
  b.prototype = Object.create(a.prototype);
  b.prototype.constructor = b;
  Object.setPrototypeOf(b, a);
  b.F = a.prototype;
}