问如何实现与ng模型( plnkr)的功能绑定

EN

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/angularjs/1.0.7/angular.min.js"></script>
<script type="text/javascript" >
    var app = angular.module('app', []);
    app.controller('AppCtrl', function ($scope) {
        $scope.dob = "2013-01-01";
        $scope.getDateOfBirth = function(dob){
            var months = ["Jan","Feb","Mar","Apr","May","June","July","Aug","Sep","Oct","Nov","Dec"]
            var split = dob.split("-");
            return parseInt(split[2])+" "+months[parseInt(split[2])-1];
        }
    });
</script>

<span ng-app="app" ng-controller="AppCtrl" ng-bind="getDateOfBirth(dob)"></span>

<input type="text" ng-model="getDateOfBirth(dob)"/>