Form submitting with Angular

I used the following codes for creating a form submit with angular $http.

HTML (in the controller div):

<input type="text" name="job" ng-model="item.job">
<button type="submit" ng-click="post()">Add</button>

JS (in the app controller):

$scope.post = function() {
            $scope.item.done = "";
            $http.post("data/todo.json", $scope.item)
                .success(function (data) {
                    console.log("OK");                  
                })
                .error(function () {
                    console.log("Sorry");                   
                });
        };

After run, it seems everything is OK and success message comes to console, but the todo.json file doesn't change!

Any Idea?