pikaday angular sending date format in json

how do i send the pikaday plugin date format in my json using ng-model

i had been trying this

<input pikaday="" ng-model="products_chosen[$index].from.getDate()" placeholder="From">

js:

    $scope.products_chosen = [{"from":new Date(),"till":new Date(),"checkbox":0}];
    $scope.productChange = function(index, checkbox){
        if(checkbox==1){
            $scope.products_chosen.push({"from":"","till":"","checkbox":0});  
        }
        else{
            $scope.products_chosen.splice(index,1);
        } 
    }