The target window of the form (target)

The target attribute of a form determines where the server response data is displayed after form submission. Proper use of target can control page navigation logic, avoid unnecessary page refreshes, or enable content updates within specific frames.

Basic Usage of the target Attribute

The target attribute is typically used in the <form> tag to specify the window where the response data will be displayed after submission. It has four standard values:

<form action="/submit" target="_blank">
  <!-- Form content -->
</form>

• _blank: Opens in a new window/tab
• _self: Opens in the current window (default)
• _parent: Opens in the parent frameset
• _top: Opens in the full window (exits frames)

Special Applications in Framed Environments

In framed pages, target can precisely control where form submissions are displayed:

<frameset cols="30%,70%">
  <frame name="nav" src="nav.html">
  <frame name="main" src="main.html">
</frameset>

<!-- In nav.html -->
<form action="search.php" target="main">
  <input type="text" name="query">
  <button>Search</button>
</form>

This example shows how to display form submission results in the right main frame while keeping the left navigation unchanged.

Modern Alternatives in Frontend Development

Although framesets are becoming obsolete, the target attribute still has special uses in modern single-page applications (SPAs):

<form action="/api/submit" target="hiddenFrame">
  <input type="email" name="email">
  <button>Subscribe</button>
</form>

<iframe name="hiddenFrame" style="display:none"></iframe>

This pattern enables form submission without refreshing the page. The server response is displayed in a hidden iframe, and JavaScript can be used to process the result:

window.addEventListener('message', (event) => {
  if (event.source === frames['hiddenFrame']) {
    console.log('Received iframe response:', event.data);
  }
});

Comparison with AJAX

Comparison between traditional target and modern AJAX submissions:

// AJAX approach
document.querySelector('form').addEventListener('submit', (e) => {
  e.preventDefault();
  fetch('/api/submit', {
    method: 'POST',
    body: new FormData(e.target)
  }).then(response => {
    // Process response
  });
});

Advantages comparison:

• target requires no JavaScript and has better compatibility
• AJAX offers more flexibility for fine-grained control of requests and responses
• target suits simple scenarios, while AJAX is better for complex interactions

Special Handling for File Uploads

Typical use of target for file uploads:

<form action="/upload" target="uploadFrame" enctype="multipart/form-data">
  <input type="file" name="file">
  <button>Upload</button>
</form>

<iframe name="uploadFrame" id="uploadFrame"></iframe>

<script>
  document.getElementById('uploadFrame').onload = function() {
    try {
      const response = this.contentDocument.body.innerText;
      console.log('Upload result:', JSON.parse(response));
    } catch(e) {}
  };
</script>

This approach avoids page refreshes while capturing the server's upload response.

Security Considerations

When using target, note the following:

1. Avoid open redirect vulnerabilities
2. When using _blank, prevent tabnabbing attacks:

<form action="/external" target="_blank" rel="noopener noreferrer">
  <!-- Secure external submission -->
</form>

3. Validate iframe content sources:

window.addEventListener('message', (event) => {
  if (event.origin !== 'https://trusted.domain') return;
  // Process message
});

Browser Compatibility Practices

Different browsers may implement target with subtle differences:

• Older IE versions may not support dynamic target changes
• Mobile browsers may handle _blank differently
• Some security settings restrict cross-frame communication

Testing example:

// Dynamically modify target
document.querySelector('form').target = 
  window.innerWidth < 768 ? '_self' : '_blank';

Interaction with CSS

target behavior may be affected by CSS:

iframe[name="hiddenFrame"] {
  width: 0; 
  height: 0;
  border: none;
  visibility: hidden;
}

Incorrect CSS settings may cause:

• Invisible iframes still occupying layout space
• Some browsers blocking content loading in zero-sized iframes
• Hidden content unexpectedly appearing in print styles

Performance Optimization Considerations

Excessive use of target="_blank" may lead to:

• Proliferation of browser tabs
• Increased memory usage
• Confusing user navigation

Optimization suggestions:

// Detect duplicate submissions
const form = document.querySelector('form');
let lastSubmit = 0;

form.addEventListener('submit', () => {
  const now = Date.now();
  if (now - lastSubmit < 1000) {
    form.target = '_self';
  }
  lastSubmit = now;
});

Accessibility Adaptations

Ensure target usage doesn't compromise accessibility:

• Provide visual cues for new window openings
• Allow users to configure whether to open in new windows
• Screen reader adaptations:

<form aria-describedby="target-description">
  <span id="target-description" class="sr-only">
    This form will open in a new window
  </span>
</form>

<style>
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}
</style>

Integration with Emerging Technologies

Using target in Web Components:

<custom-form target="custom-target">
  <!-- Shadow DOM content -->
</custom-form>

<script>
class CustomForm extends HTMLElement {
  constructor() {
    super();
    const shadow = this.attachShadow({mode: 'open'});
    shadow.innerHTML = `
      <form>
        <slot></slot>
      </form>
    `;
    this.form = shadow.querySelector('form');
  }
  
  static get observedAttributes() {
    return ['target'];
  }
  
  attributeChangedCallback(name, oldValue, newValue) {
    if (name === 'target') {
      this.form.target = newValue;
    }
  }
}

customElements.define('custom-form', CustomForm);
</script>