docs($timeout): add a $timeout example

The original example is by gxlcl.

Closes #4180

src/ng/timeout.js

@@ -31,6 +31,94 @@ function $TimeoutProvider() {
       *   will invoke `fn` within the {@link ng.$rootScope.Scope#$apply $apply} block.
       * @returns {Promise} Promise that will be resolved when the timeout is reached. The value this
       *   promise will be resolved with is the return value of the `fn` function.
+      * 
+      * @example
+      <doc:example module="time">
+        <doc:source>
+          <script>
+            function Ctrl2($scope,$timeout) {
+              $scope.format = 'M/d/yy h:mm:ss a';
+              $scope.blood_1 = 100;
+              $scope.blood_2 = 120;
+
+              var stop;
+              $scope.fight = function() {
+                stop = $timeout(function() {
+                  if ($scope.blood_1 > 0 && $scope.blood_2 > 0) {
+                      $scope.blood_1 = $scope.blood_1 - 3;
+                      $scope.blood_2 = $scope.blood_2 - 4;
+                      $scope.fight();
+                  } else {
+                      $timeout.cancel(stop);
+                  }
+                }, 100);
+              };
+
+              $scope.stopFight = function() {
+                $timeout.cancel(stop);
+              };
+
+              $scope.resetFight = function() {
+                $scope.blood_1 = 100;
+                $scope.blood_2 = 120;
+              }
+            }
+
+            angular.module('time', [])
+              // Register the 'myCurrentTime' directive factory method.
+              // We inject $timeout and dateFilter service since the factory method is DI.
+              .directive('myCurrentTime', function($timeout, dateFilter) {
+                // return the directive link function. (compile function not needed)
+                return function(scope, element, attrs) {
+                  var format,  // date format
+                  timeoutId; // timeoutId, so that we can cancel the time updates
+
+                  // used to update the UI
+                  function updateTime() {
+                    element.text(dateFilter(new Date(), format));
+                  }
+
+                  // watch the expression, and update the UI on change.
+                  scope.$watch(attrs.myCurrentTime, function(value) {
+                    format = value;
+                    updateTime();
+                  });
+
+                  // schedule update in one second
+                  function updateLater() {
+                    // save the timeoutId for canceling
+                    timeoutId = $timeout(function() {
+                      updateTime(); // update DOM
+                      updateLater(); // schedule another update
+                    }, 1000);
+                  }
+
+                  // listen on DOM destroy (removal) event, and cancel the next UI update
+                  // to prevent updating time ofter the DOM element was removed.
+                  element.bind('$destroy', function() {
+                    $timeout.cancel(timeoutId);
+                  });
+
+                  updateLater(); // kick off the UI update process.
+                }
+              });
+          </script>
+
+          <div>
+            <div ng-controller="Ctrl2">
+              Date format: <input ng-model="format"> <hr/>
+              Current time is: <span my-current-time="format"></span>
+              <hr/>
+              Blood 1 : <font color='red'>{{blood_1}}</font>
+              Blood 2 : <font color='red'>{{blood_2}}</font>
+              <button type="button" data-ng-click="fight()">Fight</button>
+              <button type="button" data-ng-click="stopFight()">StopFight</button>
+              <button type="button" data-ng-click="resetFight()">resetFight</button>
+            </div>
+          </div>
+
+        </doc:source>
+      </doc:example>
       */
     function timeout(fn, delay, invokeApply) {
       var deferred = $q.defer(),