$Watch：(监听一个model,当一个model每次改变时，都会触发第二个函数)
$watch('watchFn',watchAction,deepWatch)
watchFn：带有Angular 表达式或者函数的字符串，它会返回被监控的数据模型的当前值。
watchAction: 一个函数function(newValue,oldValue){},当watchFn 发生变化时会被调用
deepWatch:默认为false,监听数组的某个元素或者对象的属性时设置为true;
监控一个属性：
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
</head>
<body>
<div ng-app="myApp" ng-controller="myCtrl">
<form>
<div class="form-group">
<input ng-model="name" />{{name}}
<p>改变次数{{count}}</p>
</div>
</form>
</div>
<script src="http://cdn.static.runoob.com/libs/angular.js/1.4.6/angular.min.js"></script>
<script type="text/javascript">
var app = angular.module('myApp', []);
app.controller('myCtrl', function ($scope){
$scope.name = '橘子';
$scope.count = 0;
$scope.$watch('name', function (newValue, oldValue) {
$scope.count++;
if($scope.count >5){
$scope.name = '苹果';
}
});
});
</script>
</body>
</html>
监控一个对象（deepWidth为true）
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
</head>
<body>
<div ng-app="myApp" ng-controller="myCtrl">
<form>
<div class="form-group">
<input ng-model="Data.name" />{{Data.name}}
<p>改变次数{{count}}</p>
</div>
</form>
</div>
<script src="http://cdn.static.runoob.com/libs/angular.js/1.4.6/angular.min.js"></script>
<script type="text/javascript">
var app = angular.module('myApp', []);
app.controller('myCtrl', function ($scope){
$scope.Data = { name: '橘子' };
$scope.count = 0;
$scope.$watch('Data', function (newValue, oldValue) {
if(newValue == oldValue)
return;
$scope.count++;
if($scope.count >5){
$scope.Data.name = '苹果';
}
}, true);
});
</script>
</body>
</html>