HTML declare Attribute

Introduction

The declare attribute is an obsolete HTML attribute that was used with the <object> element. It indicated that the object’s properties were declared in the document but the object should not be instantiated (loaded) immediately. Modern browsers do not support this behavior, and you should not use declare in new web projects.

What You’ll Learn

Purpose of declare

The original purpose of the declare attribute was to mark an <object> as a declaration only. The browser would know about the object’s properties without loading or running the embedded resource right away. Another object could reference that declaration later. This was intended to help with performance when embedding large plugin-based content in early HTML.

📝 Syntax

Historical syntax on an <object> element:

<object data="resource.swf" type="application/x-shockwave-flash" declare>

  <p>Fallback content</p>

</object>

Syntax Rules

• Boolean attribute: presence alone meant declaration-only mode.
• Applied only to <object>, not to video, img, or script.
• No meaningful values beyond empty declare or declare="".
• Obsolete in HTML5 — treat as historical reference only.

💎 Values

Unlike many attributes, declare has no specific string values. It is a boolean attribute:

• Attribute present — Object is a declaration only (historical behavior).
• Attribute absent — Object would be instantiated normally (in legacy browsers).

<!-- Declaration only (obsolete) -->

<object data="file.pdf" type="application/pdf" declare></object>



<!-- Normal object (still valid for some embeds) -->

<object data="file.pdf" type="application/pdf"></object>

Applicable Elements

declare vs modern loading controls

Examples Gallery

Historical declare syntax, JavaScript toggle, and a modern preload alternative.

<object data="movie.mp4" type="video/mp4" declare>

  <p>Your browser does not support HTML5 video.</p>

</object>

<script>

  // Add declare

  document.getElementById("dynamicObject").setAttribute("declare", "");



  // Remove declare

  document.getElementById("dynamicObject").removeAttribute("declare");

</script>



<object id="dynamicObject" data="movie.mp4" type="video/mp4">

  <p>Fallback content</p>

</object>

<video controls preload="metadata">

  <source src="movie.mp4" type="video/mp4">

</video>

♿ Accessibility & UX

• Prefer native media — <video> and <audio> with controls are more accessible than legacy object embeds.
• Fallback content — Always include meaningful fallback inside <object> when you still use it for PDFs.
• Performance helps everyone — Lazy loading and sensible preload values reduce data use and improve experience on slow connections.
• Remove obsolete attrs — Cleaning up declare from legacy HTML simplifies maintenance without changing behavior today.

💡 Best Practices

• Since declare is obsolete and not supported by modern browsers, it is not recommended for contemporary web development.
• Consider modern alternatives such as the preload attribute on <video> and <audio>, or lazy loading techniques.
• Always test your web pages across different browsers and devices to ensure compatibility and performance.