mvc inside of javascript

I tried to get mvc class inside of javascript like below. but it alerts that fixed up with javascript codes. Is it a way to use mvc inside of javascript?

@MasterHelper.Generic.DecryptPassword(data[index].passcode);

 function UserInfo()
    {
        var userid = localStorage.getItem("userid");
        $(document).ready(function () {
            $.ajax({
                url: "/Api/UserInfo",
                datatype: "text",
                type: "POST",
                data: { 'userid': userid},
                dataType: 'json',
                success: function (data) {
                    $.each(data, function (index) {
                        var test = data[index].passcode; 
                        document.getElementById("firstname").value = data[index].firstname; 
                        document.getElementById("lastname").value = data[index].lastname; 
                        document.getElementById("passcode").value = @MasterHelper.Generic.DecryptPassword(data[index].passcode); 
                        document.getElementById("emailadr").value=data[index].email;                            
                    });
                },
                error: function (msg) { alert(msg); }
            });
        }); 
    }

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