ajax提交带附件的表单

var randomVar = Math.round(Math.random() * (9999999999+1) - 0.5);
    var boundary = 90000000000 + randomVar;
    $.ajax({
            contentType: "multipart/form-data; charset=UTF-8;boundary=boundary",
            url: url,
            type: 'post',
            dataType: 'text',
            data: $("#myform").serialize(),
            error: function(){
                 alert('操作失败');
            },
            success: function(reMsg){
                if(reMsg.match("ture")!=null){
                    reMsg = reMsg.replace("true+","")
                    $("#sb_dealId").val(reMsg);
                }
            }
        });