References

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

The HTML onloadeddata event

Event All modern browsers Updated
Quick answer

The HTML onloadeddata attribute runs JavaScript when the first frame of the media has loaded. It is an inline handler for the loadeddata event; in modern code prefer addEventListener('loadeddata', …).

Overview

The onloadeddata event attribute runs JavaScript when the first media frame is available. In JavaScript the event itself is named loadeddata — 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 onloadeddata HTML attribute, but the modern, recommended approach is element.addEventListener('loadeddata', 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 onloadeddata="handler()">…</element>

element.addEventListener('loadeddata', handler);

Best practices

  • Prefer element.addEventListener('loadeddata', handler) over the inline onloadeddata 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 onloadeddata event?
It runs JavaScript when the first media frame is available. In JavaScript the event is named loadeddata.
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 onloadeddata attribute or addEventListener?
Prefer addEventListener('loadeddata', …) in JavaScript. The inline onloadeddata attribute works but mixes behavior into the markup and allows only one handler per element.
onload onloadedmetadata