References

Beginner-friendly references for web development, with live, editable examples.

The HTML onloadedmetadata event

Event All modern browsers Updated
Quick answer

The HTML onloadedmetadata attribute runs JavaScript when the media's metadata (duration, dimensions) has loaded. It is an inline handler for the loadedmetadata event; in modern code prefer addEventListener('loadedmetadata', …).

Overview

The onloadedmetadata event attribute runs JavaScript when media metadata is available. In JavaScript the event itself is named loadedmetadata — drop the on prefix when you call addEventListener.

It is one of the media events, fired by <audio> and <video> elements as their loading and playback state changes. These events drive custom players — progress bars, buffering spinners, play/pause UI.

You can wire this up with the inline onloadedmetadata HTML attribute, but the modern, recommended approach is element.addEventListener('loadedmetadata', handler) in JavaScript. That keeps behavior out of your markup, lets you attach several handlers to the same event, and makes them easy to remove. The inline attribute is fine for quick demos.

Syntax

<element onloadedmetadata="handler()">…</element>

element.addEventListener('loadedmetadata', handler);

Best practices

  • Prefer element.addEventListener('loadedmetadata', handler) over the inline onloadedmetadata attribute — it separates behavior from markup and allows multiple handlers.
  • Attach media events to the <video>/<audio> element to build custom player UI.
  • Read the element's state (currentTime, duration, buffered) inside the handler.
  • Still provide native controls and captions for accessibility.

Frequently asked questions

What is the onloadedmetadata event?
It runs JavaScript when media metadata is available. In JavaScript the event is named loadedmetadata.
Which elements fire this event?
Media elements — <audio> and <video> — as their playback or loading state changes.
How do I build a custom video player?
Listen to the media events and read/set properties like currentTime and paused on the element to drive your own controls.
Should I use the onloadedmetadata attribute or addEventListener?
Prefer addEventListener('loadedmetadata', …) in JavaScript. The inline onloadedmetadata attribute works but mixes behavior into the markup and allows only one handler per element.
onloadeddata onloadstart