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我想检查我的姓氏元素是否具有“If”语句的信息，但我不知道该把它放在哪里，或者如果我正在讨论这个错误。目的是在我能够点击提交按钮之前最终检查是否所有的框都已填满。那么最好的方法去检查这个呢？检查表单中是否有信息
function check() {
let lastName = document.findElementById('last-name').value;
addressForm = document.shippingAddressForm;
addressForm.addEventListener('submit', (event) => {
event.preventDefault();
});
alert("Please enter all fields ");
}<head>
<meta charset="utf-8">
<title>JavaScript</title>
<link href="style.css" rel="stylesheet">
<script src="main.js" defer></script>
</head>
<body>
<form id="shipping-address-form" name="shippingAddressForm" action="#" method="post">
<h1>Shipping Address</h1>
<div class="flex-container">
<div>
<label for="first-name">First Name:</label>
<input type="text" id="first-name" name="firstName" />
</div>
<div>
<label for="last-name">Last Name:</label>
<input type="text" id="last-name" name="lastName" />
</div>
</div>
<div class="flex-container">
<label for="address">Address:</label>
<input type="text" id="address" name="address" />
</div>
<div class="flex-container">
<div>
<label for="city">City:</label>
<input type="text" id="city" name="city" />
</div>
<div>
<label for="state">State:</label>
<input type="state" id="state" name="state" />
</div>
<div>
<label for="zip-code">Zip Code:</label>
<input type="text" id="zip-code" name="zipCode" />
</div>
</div>
<div class="flex-container">
<div>
<label for="phone-number">Phone Number:</label>
<input type="text" id="phone-number" name="phoneNumber" />
</div>
<div>
<label for="email">Email:</label>
<input type="text" id="email" name="email" />
</div>
</div>
<div class="button">
<button type="submit">Submit</button>
</div>
</form>
</body>
此链接可能会帮助https://www.w3schools.com/js/js_validation.asp –
你也可以尝试使用'required'属性：HTTPS：//www.w3schools的.com /标签/ att_input_required.asp –