how to disable previous dates in calendar?

Question

I am trying to disable previous dates in calendar.I am using this code like

My HTML code is below.

<div class="date-picker">
<div class="input">
    <div class="result"><input type="text" class="xxy" value="<?= $c_date1; ?>" ></div>
</div>
<div class="calendar"></div>

My script code.

$(function() {
  $(".calendar").datepicker({
        dateFormat: 'dd/mm/yy',
        firstDay: 1
    });

    $(document).on('click', '.date-picker .input', function(e){
        var $me = $(this),
        $parent = $me.parents('.date-picker');
        $parent.toggleClass('open');


    });


    $(".calendar").on("change",function(){
        var $me = $(this),
            $selected = $me.val(),
            $parent = $me.parents('.date-picker');
            console.log($parent);
            $parent.find('.result').children('input').val($selected);
    });
});