FormData不能用 jquery获取表单对象 ，一定要用原生的js语法

FormData不能用 jquery获取表单对象，一定要用原生的js语法！！！！否则抓取不到数据

$('#modal_form').validate({
	submitHandler: function(form) {
		var formobj =  document.getElementById("modal_form");    //一定要原生js语法获取form表单dom
		var res = new FormData(formobj);
		$.ajax({
			url: "<?php echo $this->config->app_url_root.'/Goods/ajax_add_brand'?>",
			type: "POST",
			dataType:"json",            
			data: res,
			cache: false,
			contentType: false,       //一定要写  
			processData: false,       //一定要写
			success: function(e) {
				e = JSON.parse(e);
				console.log(e);
			}
		});
		return false;
	},
	rules: {
		brand_name: "required",
		brand_desc: "required",
		site_url: {
			required: true,
			url: true
		}
	} 
});

图示：