A.js

define(function (require) {
  var B = require('./B');
  return function () {
    B();
  };
});

B.js

define(function (require) {
  var A = require('./A');
  return function () {
    A();
  };
});

C.js

define(function (require, exports) {
  var D = require('./D');
  
  exports.default = function () {
    D.default();
  };
});

D.js

define(function (require, exports) {
  var C = require('./C');
  
  exports.default = function () {
    C.default();
  };
});