表单不写参数时所传的参数类型

为空值，判断条件用==""

 

example

In JSP:

                            <select name="severity">                           
                                <option selected>------------ 
                                <option value="L">LOW
                                <option value="M">MIDDLE
                                <option value="H">HIGH
                            </select>

 

In Javascript:

 

        if(false && document.AppForm.severity.value=="")

            alert("none select")