Circular dependency

ModuleA.js

import can from 'can';
import {B} from './ModuleB';

export let A = {
  a: 1
};

export let ExtendedA = can.extend({}, A, {
  a2: B
});

export default ExtendedA;

ModuleB.js

import can from 'can';
import {A} from './ModuleA';

export let B = {
  b: 2
};

export let ExtendedB = can.extend({}, B, {
  b2: A
});

export default ExtendedB;