AngularJS $watch not working properly - angularjs

Question

Recently I am learning Angularjs, my code seems not work as expected:
this is my div:
<div ng-app="myApp">
<div ng-controller="myController">
<input type="text" ng-model="data.name" value=""/>
{{data.count}}
</div>
</div>
my controller is:
<script>
var app = angular.module('myApp',[]);
app.controller('myController', function($scope) {
$scope.data = {
name:"tom",
count = 0
}
$scope.$watch('data', function(oldValue,newValue) {
++$scope.data.count;
},true);
})
</script>
what I expect is when I type something in the <input> box, the {{data.count}} will increase by 1 each time. However the code is initially 11 and each time I make changes in the input field, the count is increased by 11, can someone help me find where have I done wrong? Thanks a lot in advance.

Answer 1

Why this happen?
Watcher calls multiple times because you created watcher for full object data. Flag true will create sub-watcher for every value in object.
Its a proper behavior. I believe you want something like:
$scope.$watch('data', function(oldValue,newValue) {
if(oldValue.name != newValue.name){
++$scope.data.count;
}
},true);
Demo Fiddle
The second solution is to watch on name only:
$scope.$watch(function(){
return $scope.data.name
}, function(oldValue,newValue) {
++$scope.data.count;
});

Answer 2

Here is a another way to do it. Use the ng-keydown directive and update the count only when a key is pressed inside the input element.
var app = angular.module('myApp', []);
app.controller('MyController', function MyController($scope) {
$scope.data = {
name: "tom",
count: 0
}
});
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-controller='MyController' ng-app='myApp'>
<input type="text" ng-model="data.name" value="" ng-keydown="data.count = data.count+1" /> {{data.count}}
</div>