Difference between two datepicker in Backbonejs

Question

Can anyone tell me how to make difference between two datepickers in backbonejs ? I try to make it like that in my view but it alerts a NAN :

initialize: function () {

 this.model.on("change:auprov",function(){
                       var datedeb = new Date(this.model.get("auprov"));
                       var dateret = new Date(this.model.get("deprov"));
                       var diff_ms = dateret.getTime() - datedeb.getTime();
                       alert(diff_ms/1000/60/60/24);
                       //this.model.set({"dureeprov": '5'});
                                        },this);
    },

Here is a part of my model :

deprov:{
type: "DatePicker",
title: "De (Prov.)",
fieldAttrs:{
        className:'col-sm-2 deprov'
    },
validators: ["required"]
  },
auprov:{
type: "DatePicker",
title: "Au (Prov.)",
fieldAttrs:{
        className:'col-sm-2 auprov'
    },
validators: ["required"]
  },

Regards

Answer 1

Sorry I was using French datepicker form, so i had to change it to english one, here the correct code :

this.model.on("change:auprov",function(){
        var myDateArrayRet = this.model.get("auprov").split("/");
        var dateret = new Date(myDateArrayRet[2],myDateArrayRet[1]-1,myDateArrayRet[0]);
        var myDateArray = this.model.get("deprov").split("/");
        var datedeb = new Date(myDateArray[2],myDateArray[1]-1,myDateArray[0]);
        var diff_ms = dateret.getTime() - datedeb.getTime();
        alert(Math.ceil(diff_ms / (1000 * 3600 * 24)));
        },this);