@ngdoc overview
@name Cookbook: MVC
@description

MVC allows for a clean and testable separation between the behavior (controller) and the view
(HTML template). A Controller is just a JavaScript class which is grafted onto the scope of the
view. This makes it very easy for the controller and the view to share the model.

The model is a set of objects and primitives that are referenced from the Scope ($scope) object.
This makes it very easy to test the controller in isolation since one can simply instantiate the
controller and test without a view, because there is no connection between the controller and the
view.


<doc:example>
  <doc:source>
    <script>
    function TicTacToeCntl($scope, $location) {
      $scope.cellStyle= {
        'height': '20px',
        'width': '20px',
        'border': '1px solid black',
        'text-align': 'center',
        'vertical-align': 'middle',
        'cursor': 'pointer'
      };

      $scope.reset = function() {
        $scope.board = [
          ['', '', ''],
          ['', '', ''],
          ['', '', '']
        ];
        $scope.nextMove = 'X';
        $scope.winner = '';
        setUrl();
      };

      $scope.dropPiece = function(row, col) {
        if (!$scope.winner && !$scope.board[row][col]) {
          $scope.board[row][col] = $scope.nextMove;
          $scope.nextMove = $scope.nextMove == 'X' ? 'O' : 'X';
          setUrl();
        }
      };

      $scope.reset();
      $scope.$watch(function() { return $location.search().board;}, readUrl);

      function setUrl() {
        var rows = [];
        angular.forEach($scope.board, function(row) {
          rows.push(row.join(','));
        });
        $location.search({board: rows.join(';') + '/' + $scope.nextMove});
      }

      function grade() {
        var b = $scope.board;
        $scope.winner =
          row(0) || row(1) || row(2) ||
          col(0) || col(1) || col(2) ||
          diagonal(-1) || diagonal(1);
        function row(row) { return same(b[row][0], b[row][1], b[row][2]);}
        function col(col) { return same(b[0][col], b[1][col], b[2][col]);}
        function diagonal(i) { return same(b[0][1-i], b[1][1], b[2][1+i]);}
        function same(a, b, c) { return (a==b && b==c) ? a : '';};
      }

      function readUrl(value) {
        if (value) {
          value = value.split('/');
          $scope.nextMove = value[1];
          angular.forEach(value[0].split(';'), function(row, col){
            $scope.board[col] = row.split(',');
          });
          grade();
        }
      }
    }
    </script>

    <h3>Tic-Tac-Toe</h3>
    <div ng-controller="TicTacToeCntl">
    Next Player: {{nextMove}}
    <div class="winner" ng-show="winner">Player {{winner}} has won!</div>
      <table class="board">
        <tr ng-repeat="row in board track by $index" style="height:15px;">
          <td ng-repeat="cell in row track by $index" ng-style="cellStyle"
              ng-click="dropPiece($parent.$index, $index)">{{cell}}</td>
        </tr>
      </table>
      <button ng-click="reset()">reset board</button>
    </div>
  </doc:source>
  <doc:scenario>
    it('should play a game', function() {
     piece(1, 1);
     expect(binding('nextMove')).toEqual('O');
     piece(3, 1);
     expect(binding('nextMove')).toEqual('X');
     piece(1, 2);
     piece(3, 2);
     piece(1, 3);
     expect(element('.winner').text()).toEqual('Player X has won!');
    });

    function piece(row, col) {
      element('.board tr:nth-child('+row+') td:nth-child('+col+')').click();
    }
  </doc:scenario>
</doc:example>


# Things to notice

* The controller is defined in JavaScript and has no reference to the rendering logic.
* The controller is instantiated by Angular and injected into the view.
* The controller can be instantiated in isolation (without a view) and the code will still execute.
This makes it very testable.
* The HTML view is a projection of the model. In the above example, the model is stored in the
board variable.
* All of the controller's properties (such as board and nextMove) are available to the view.
* Changing the model changes the view.
* The view can call any controller function.
* In this example, the `setUrl()` and `readUrl()` functions copy the game state to/from the URL's
hash so the browser's back button will undo game steps. See deep-linking. This example calls {@link
api/ng.$rootScope.Scope#$watch $watch()} to set up a listener that invokes `readUrl()` when needed.