HTML classid Attribute

Introduction

The classid attribute in HTML is used with the <object> element to specify the location or identifier of an object’s implementation, typically for embedding ActiveX controls in legacy web pages. It was more common in older versions of Internet Explorer and has largely been deprecated in modern web development due to security concerns and the shift toward standardized HTML5 technologies.

What You’ll Learn

Purpose of classid Attribute

The primary purpose of the classid attribute is to define the URI or programmatic identifier (CLSID) of the embedded object that the browser should load. It tells the browser where to find the code necessary to run the plugin or control—historically ActiveX in Internet Explorer.

📝 Syntax

Add classid to an <object> element with a URI or CLSID value:

<object classid="clsid:XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX" width="400" height="300">
  <p>Fallback content</p>
</object>

Syntax Rules

• Used on <object> (and legacy <applet>).
• Value is a URI—often clsid: followed by a GUID for ActiveX.
• Pair with <param> elements to pass configuration to the control.
• Always include fallback content inside <object>.
• For modern media, prefer data on object, or <video>, <iframe>.

💎 Values

The value of the classid attribute is typically a URI that points to the object implementation. Common forms include:

URL

Specifies the location of the object implementation:

<object classid="http://www.example.com/someobject">
  <p>Fallback</p>
</object>

CLSID (ProgID / ActiveX)

A unique identifier for a COM/ActiveX control:

<object classid="clsid:XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX">
  <p>Fallback</p>
</object>

Applicable Elements

Examples Gallery

URL and CLSID classid values, object with param, and dynamic JavaScript classid.

<object classid="http://www.example.com/someobject" width="300" height="200">
  <p>Your browser does not support this object.</p>
</object>

<object classid="clsid:CLSID-ExampleID" width="400" height="300">
  <param name="paramName" value="paramValue">
  <p>Your browser does not support embedded objects.</p>
</object>

<object id="dynamicObject" width="200" height="100">
  Your browser does not support this object.
</object>

<script>
  document.getElementById("dynamicObject").classid =
    "clsid:NEW-EXAMPLE-ID";
</script>

♿ Accessibility

• Provide fallback content — Always include accessible text inside <object> when plugins fail.
• Avoid plugin-only features — Do not rely on ActiveX for essential functionality.
• Use native HTML — Video, audio, and canvas are more accessible than legacy plugins.
• Title attributes — Describe embedded content when using iframes as replacements.
• Keyboard access — Plugin content often lacked proper keyboard support.

💡 Best Practices

• Security considerations: Due to vulnerabilities associated with ActiveX controls, modern web development generally avoids the classid attribute.
• Browser compatibility: classid is not supported by most modern browsers. Provide alternative content for all users.
• Deprecation: classid for ActiveX is obsolete. Use current methods such as <embed>, <iframe>, or native HTML5 elements.