Share data between AngularJS controllers

A simple solution is to have your factory return an object and let your controllers work with a reference to the same object:

JS:

// declare the app with no dependencies
var myApp = angular.module('myApp', []);

// Create the factory that share the Fact
myApp.factory('Fact', function(){
  return { Field: '' };
});

// Two controllers sharing an object that has a string in it
myApp.controller('FirstCtrl', function( $scope, Fact ){
  $scope.Alpha = Fact;
});

myApp.controller('SecondCtrl', function( $scope, Fact ){
  $scope.Beta = Fact;
});

HTML:

<div ng-controller="FirstCtrl">
    <input type="text" ng-model="Alpha.Field">
    First {{Alpha.Field}}
</div>

<div ng-controller="SecondCtrl">
<input type="text" ng-model="Beta.Field">
    Second {{Beta.Field}}
</div>

Demo: http://jsfiddle.net/HEdJF/

When applications get larger, more complex and harder to test you might not want to expose the entire object from the factory this way, but instead give limited access for example via getters and setters:

myApp.factory('Data', function () {

    var data = {
        FirstName: ''
    };

    return {
        getFirstName: function () {
            return data.FirstName;
        },
        setFirstName: function (firstName) {
            data.FirstName = firstName;
        }
    };
});

With this approach it is up to the consuming controllers to update the factory with new values, and to watch for changes to get them:

myApp.controller('FirstCtrl', function ($scope, Data) {

    $scope.firstName="";

    $scope.$watch('firstName', function (newValue, oldValue) {
        if (newValue !== oldValue) Data.setFirstName(newValue);
    });
});

myApp.controller('SecondCtrl', function ($scope, Data) {

    $scope.$watch(function () { return Data.getFirstName(); }, function (newValue, oldValue) {
        if (newValue !== oldValue) $scope.firstName = newValue;
    });
});

HTML:

<div ng-controller="FirstCtrl">
  <input type="text" ng-model="firstName">
  <br>Input is : <strong>{{firstName}}</strong>
</div>
<hr>
<div ng-controller="SecondCtrl">
  Input should also be here: {{firstName}}
</div>

Demo: http://jsfiddle.net/27mk1n1o/