javascript - 设置表单验证功能时遇到问题

Question

<td> <label> Gender: </label> </td>
<td> <select> id="gender" name = "gender">
                        <option>Select a gender</option>
                        <option>Male</option>
                        <option>Female</option>
                     </select>
                </td>

这就是我试图验证的表单，这是我的 javascript，但我看不到让它工作:

function validateGender(){
                if("" == document.getElementsByID('gender')[0].selectedIndex){
                    alert("Please select a gender")
                    return;
}
            }

Answer 1

function validateGender(){
                if(document.getElementById("gender").selectedIndex==0){
                    alert("Please select a gender");
                    return;
}

            }

<select id="gender" name = "gender">
                        <option>Select a gender</option>
                        <option value="male">Male</option>
                        <option value="female">Female</option>
                     </select>
                     <button onclick="validateGender()">validate</button>

检查一下。