Javascript ile fiyat tablosu hakkında

    setInterval(
            function check()
            {
                var dif1 = new Date(document.getElementById("checkinx").value);
                var dif2 = new Date(document.getElementById("checkoutx").value);

                var diff_in_time = dif2.getTime() - dif1.getTime();
                var diff_in_days = diff_in_time / (1000*3600*24);
                
                if(diff_in_days < 4){
                    
                    console.log("4 günden küçük");
                    correct();    
                }
            }
        , 100);
    function correct(){
        var dateCorrect = new Date(document.getElementById("checkinx").value);
        dateCorrect.setDate((dateCorrect.getDate()+4));
        dateCorrect = dateCorrect.toISOString().slice(0,10);
        document.getElementById("checkoutx").value = dateCorrect;
    }
    function set(){
        var today = new Date().toISOString().slice(0,10);
        document.getElementById("checkinx").value = today;

        var date2 = new Date;
        date2.setDate(date2.getDate()+4);
        var day4 = date2.toISOString().slice(0,10);
        document.getElementById("checkoutx").value = day4;
    }