Calculate number of months between two dates using javascript

<script>

    var dtfrm ='10/01/2019';//////////dd/mm/yyyy

    var dtto = '31/03/2019';

    var d1 = dtfrm.split('/');

    var d2 = dtto.split('/');

    var frstdate = new Date(d1[2], (parseFloat(d1[1]) - 1).toFixed(0), d1[0]);

    var secdate = new Date(d2[2], (parseFloat(d2[1]) - 1).toFixed(0), d2[0]);

    if (frstdate > secdate) {

        var dtothr;

        dtothr = frstdate;

        frstdate = secdate;       

        secdate = dtothr;

    }

    var mnth = ((secdate.getFullYear() * 12 + secdate.getMonth()) - (frstdate.getFullYear() * 12 + frstdate.getMonth()));

  

    alert(mnth);

</script>

Result///