code Js input - Kiểm tra field

 **** HTML

<form action="" method="POST" role="form" name="fromdathang">

    <legend>Form title</legend>

    <div class="form-group">

        <label for="">label</label>

        <input type="text" class="form-control" placeholder="Input field" name="txt_email">

    </div>

    <button type="submit" class="btn btn-primary">Submit</button>

</form>

**** JS

$('#save__muahang').submit(function(e) {

    

    // e.preventDefault();

    data = new FormData($('#save__muahang')[0]);

    if(kiemtra()==true){

        $(".waiting").show();

        $("body").addClass("modal-open");

        $(".sendmail").addClass("modal-backdrop fade in");

        $.ajax({

            type: 'POST',

            url: '/op=save__muahang',

            data: data,

            cache: false,

            contentType: false,

            processData: false

        }).done(function(data) {

            if(data==1){

                $(".waiting").hide();

                $("body").removeClass("modal-open");

                $(".sendmail").removeClass("modal-backdrop fade in");

                $('.muahangthanhcong').addClass("error");    

                $('.muahangthanhcong').addClass("is-active");    

                load_muahang();

            }else{

                console.log(data);

            }

        }).fail(function(jqXHR,status, errorThrown) {

            console.log(errorThrown);

            console.log(jqXHR.responseText);

            console.log(jqXHR.status);

        });

    }    

});

function kiemtra(){

    /**test**/

    let u = document.fromdathang.txt_email.value;

    let hoten = document.fromdathang.txt_hoten.value;

    let dt = document.fromdathang.txt_dienthoai.value;

    let dc = document.fromdathang.txt_diachi.value;

    let tinh = document.fromdathang.customer_shipping_province.value;

    let ward = document.fromdathang.customer_shipping_district.value;

    let pho = document.fromdathang.customer_shipping_phuongxa.value;

    let note = document.fromdathang.txt_ghichu.value;

    let cod = document.fromdathang.cod.value;

    let magg = document.fromdathang.txt_magiamgia.value;

    let ship = document.fromdathang.txt_freeship.value;    

    if (u=="") { //quy tắc 1

        // console.log("not-email");

        location.href = "/op=save__gialap&txt_hoten="+hoten+"&txt_dienthoai="+dt+"&txt_diachi="+dc+"&customer_shipping_province="+tinh+"&customer_shipping_district="+ward+"&customer_shipping_phuongxa="+pho+"&txt_ghichu="+note+"&cod="+cod+"&txt_magiamgia="+magg+"&txt_freeship="+ship+"";

        return;

    }

    return true;

}