客户端验证显示问题

Question

我是JavaScript的新手，我正在尝试在我的注册表单上实现客户端验证。目标是当用户按下提交按钮时，错误被设置为可见性：可见。但是这不起作用。我的代码出了什么问题？

function validate() {
    var errorname = document.getElementById("errorforename");
    var user_forename = document.register.user_forename;
    if (user_forename === "") {
        errorforename.style.visibility = "visible";
    }
}

.error {
    color: red;
    font-style: italic;
    font-size: 17px;
    visibility: hidden;
}

    <form id="register" name="register" action="#" method="post">

    <label for="forename">Forename</label>
                <input type="text" id="forename" name="user_forename" placeholder="John" required>
                <span id="errorforename" class="error">First name is required</span>
     <button type="submit" value="Submit" onclick="validate();">Register</button>

    </form>

Answer 1

document.register.user_forename是元素。要阅读其值，您需要添加.value。

Answer 2

在 document.register.user_forename 之后添加 .value ，

像这样，var user_forename = document.register.user_forename.value;