function interest_model_change() {

    var model = $("#interestModel").val();

    var installments = document.getElementById("installments");

    var daysDiv = document.getElementById("daysDiv");

    if (model == "daily") {

        //select联动onchange后修改installments默认值，此时使用jquery$(selector).val()方法更加安全

        $("#installments").val("1");

        $("#installments").attr("readonly", "true");

        daysDiv.removeAttribute("hidden");

    } else {

        $("#installments").val("12");

        installments.removeAttribute("readonly");

        daysDiv.setAttribute("hidden", "");

    }

}