javascript - 如何验证 HTML 表单？

Question

我有一个 HTML 表单和一个按钮，当用户单击该按钮时将检查表单是否已填写。帐单地址的详细信息是使用 php 从数据库输入的

<button id="btnConfirm" type="submit" onclick="validate()"style="float: right" value="Confirm Payment" >Confirm Payment</button>
<form id="au" name="paymentform" method="post" action="" >
<fieldset class="billing">
<legend>Billing Details</legend>
<br />
<label class="reglabel" for="fname">First Name:</label>
<input id="fname" name="billingfname" required="" type="text" value="<?php echo $fname ?>" /><br />
<label class="reglabel" for="lname">Last Name:</label>
<input id="lname" name="billinglname" required="" type="text" value="<?php echo $lname ?>" /><br />
<label class="reglabel" for="address">Address:</label>
<input id="address" name="billingaddress" required="" type="text" value="<?php echo $address ?>" /><br />
<label class="reglabel" for="town">Town:</label>
<input id="town" name="billingtown" required="" type="text" value="<?php echo $town ?>" /><br />
<label class="reglabel" for="postcode">Post Code:</label>
<input id="postcode" name="billingpostcode" required="" type="text" value="<?php echo $postcode ?>" /><br />
<label class="reglabel" for="phone">Phone:</label>
<input id="phone" name="billingphone" required="" type="text" value="<?php echo $phone ?>" /><br />
<label id="EmailLabel" class="reglabel" for="email">E-mail:</label>
<input id="email" name="billingemail" required="" type="email" value="<?php echo $email ?>" /><br />
</fieldset> 
<fieldset class="shipping">
<legend>Shipping Details</legend>
<br />
<input name="shippingsame" onclick="fillShipping(this.form)" type="checkbox">Check 
    this box if billing address and shipping address are the same <br />
<label class="reglabel" for="fname">First Name:</label>
<input id="fname" name="shippingfname" placeholder="Required" required="" type="text" /><br />
<label class="reglabel" for="lname">Last Name:</label>
<input id="lname" name="shippinglname" placeholder="Required" required="" type="text" /><br />
<label class="reglabel" for="address">Address:</label>
<input id="address" name="shippingaddress" placeholder="Required" required="" type="text" /><br />
<label class="reglabel" for="town">Town:</label>
<input id="town" name="shippingtown" placeholder="Required" required="" type="text" /><br />
<label class="reglabel" for="postcode">Post Code:</label>
<input id="postcode" name="shippingpostcode" placeholder="Required" required="" type="text" /><br />
<label class="reglabel" for="phone">Phone:</label>
<input id="phone" name="shippingphone" placeholder="Required" required="" type="text" /><br />
<label id="EmailLabel" class="reglabel" for="email">E-mail:</label>
<input id="email" name="shippingemail" placeholder="Required" required="" type="email" /><br />
</fieldset> 
   </form>

这是我试图检查字段是否为空的代码，但它似乎不起作用。它警告未定义

function validate()
{
var firstname = document.getElementsByName("shippingfname").value;
if (firstname == "")
{
    alert('empty'); 
}   
else
{
    alert(firstname);
}
}

Answer 1

函数document.getElementsByName返回一个数组，所以你应该尝试这个:

function validate()
{
var firstname = document.getElementsByName("shippingfname")[0].value;
if (firstname == "")
{
    alert('empty'); 
}   
else
{
    alert(firstname);
}
}