Circular dependency problem and its solutions for node.js

a.js

"use strict";

var B = require('./b');

var A = module.exports = (function() {
  var id, bInstance;

  return {
    init: function init(val) {
      id = val;
      bInstance = new B();
      return this;
    },

    doStuff: function doStuff() {
      bInstance.stuff();
      return this;
    },

    getId: function getId() {
      return id;
    }
  };
}());

a_di.js

// solution 3: dependency injection
"use strict";

var B = require('./b');

var A = module.exports = (function() {
  var id, bInstance;

  return {
    init: function init(val) {
      id = val;
      bInstance = new B(this); // 注目!
      return this;
    },

    doStuff: function doStuff() {
      bInstance.stuff();
      return this;
    },

    getId: function getId() {
      return id;
    }
  };
}());
[Hoover:

a_lazyrequire.js

// solution 2: lazy require 
"use strict";

var A = module.exports = (function() {
  var id, bInstance;

  return {
    init: function init(val) {
      id = val;
      bInstance = (new require('./b'))(); // 注目!
      return this;
    },

    doStuff: function doStuff() {
      bInstance.stuff();
      return this;
    },

    getId: function getId() {
      return id;
    }
  };
}());

a_module.exports_first.js

// solution 1: module.exports first
"use strict";

var A = module.exports = {}; // 注目!

var B = require('./b');

var id, bInstance;

A.init = function init(val) {
  id = val;
  bInstance = new B();
  return this;
};

A.doStuff = function doStuff() {
  bInstance.stuff();
  return this;
};

A.getId = function getId() {
  return id;
};

b.js

"use strict";

var A = require('./a');

var B = module.exports = function() {
  return {
    stuff: function stuff() {
      console.log('I got the id: ', A.getId());
    }
  };
};

b_di.js

"use strict";

var B = module.exports = function(A) {
  var DI = A;
  return {
    stuff: function stuff() {
      console.log('I got the id: ', DI.getId()); // 注目！
    }
  };
};

main.js

"use strict";

var A = require('./a')
A.init(1234).doStuff();