JavaScript references make Angular hell.

test.js

function controllerOne(varA) {
  var vm = this;
  vm.a = varA;

  vm.printA = function() {
    console.log('A is: ', vm.a)
  }

  vm.setA = function(a) {
    vm.a.a = a;
    console.log('A is: ', vm.a)
  }
}

function controllerTwo(varB) {
  var vm = this;
  vm.b = varB;

  vm.printB = function() {
    console.log('B is: ', vm.b)
  }

  vm.setB = function(b) {
    vm.b = b;
    console.log('B is: ', vm.b)
  }
}

// Our mock data.
var a = { a: 'a' };

// Create our two controllers so they're using our mock data.
var num1 = new controllerOne(a);
var num2 = new controllerTwo(a);

// Prove that they're using the mock data.
num1.printA();
num2.printB();

// Mutate data within the data structure.
num1.setA('foo');

// Show that it reflects in the second controller.
num2.printB();

// Now change the data structure within B.
num2.setB({a: 'b'});

// Show that it's changed in B.
num2.printB();

// And that A is now orphaned:
num1.printA();