องค์ประกอบ form: action, method และ enctype

ฟอร์มคืออะไร

องค์ประกอบ form

<form action="/submit" method="post">
  <!-- form controls go here -->
  <button type="submit">Send</button>
</form>
<!-- When the user submits, the browser sends the form data
     to the URL specified in action using the method specified -->

แอตทริบิวต์ action

<form action="/api/login">...</form>      <!-- relative path -->
<form action="https://api.example.com/form">...</form>  <!-- absolute -->
<form action="">...</form>                 <!-- current URL (empty) -->
<form>...</form>                           <!-- no action = current URL -->

แอตทริบิวต์ method

<form method="get">...</form>
<!-- GET: appends data to URL as query string
     example.com/search?q=html&sort=date
     Used for: search forms, filters, bookmarkable results -->

<form method="post">...</form>
<!-- POST: sends data in the request body
     Data is not visible in the URL
     Used for: login, registration, file uploads, sensitive data -->

GET เทียบกับ POST

แอตทริบิวต์ enctype

<!-- Default: URL-encoded (text/form fields) -->
<form method="post" enctype="application/x-www-form-urlencoded">

<!-- For file uploads: multipart -->
<form method="post" enctype="multipart/form-data">
  <input type="file" name="avatar">
</form>

<!-- Plain text (rare): -->
<form method="post" enctype="text/plain">

แอตทริบิวต์ novalidate

<form action="/submit" method="post" novalidate>
  <!-- Validation handled by JavaScript instead -->
  <input type="email" name="email">
  <button type="submit">Submit</button>
</form>

แอตทริบิวต์ target ในฟอร์ม

<form action="/search" target="_blank">
  <!-- Response opens in a new tab -->
</form>
<!-- Values: _blank, _self, _parent, _top, or a frame name -->
<!-- Rarely used — most forms stay on the same page or use AJAX -->

autocomplete ในฟอร์ม

<!-- Off: disable autofill for the entire form -->
<form autocomplete="off">

<!-- On (default): allow autofill -->
<form autocomplete="on">

<!-- Better: control at the field level:
<input type="email" autocomplete="email">
<input type="current-password" autocomplete="current-password">
-->

การส่งฟอร์มด้วย JavaScript

<form id="contact-form" action="/contact" method="post">
  <input type="text" name="name">
  <button type="submit">Send</button>
</form>

<script>
document.getElementById('contact-form').addEventListener('submit', async (e) => {
  e.preventDefault();  // stop normal browser submission
  const data = new FormData(e.target);
  const res = await fetch('/contact', { method: 'POST', body: data });
  // handle response...
});
</script>

action และ method ร่วมกัน

<form action="/api/newsletter" method="post">
  <label for="email">Email address</label>
  <input type="email" id="email" name="email" required>
  <button type="submit">Subscribe</button>
</form>
<!-- POST because: creating a subscription = server state change -->

ตรวจสอบความเข้าใจ

ทบทวน: องค์ประกอบ form