References

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

The HTML oncanplaythrough event

Event All modern browsers Updated
Quick answer

The HTML oncanplaythrough attribute runs JavaScript when the browser estimates it can play the media to the end without buffering. It is an inline handler for the canplaythrough event; in modern code prefer addEventListener('canplaythrough', …).

Overview

The oncanplaythrough event attribute runs JavaScript when media can play through without stopping. In JavaScript the event itself is named canplaythrough — 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 oncanplaythrough HTML attribute, but the modern, recommended approach is element.addEventListener('canplaythrough', 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 oncanplaythrough="handler()">…</element>

element.addEventListener('canplaythrough', handler);

Best practices

  • Prefer element.addEventListener('canplaythrough', handler) over the inline oncanplaythrough 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 oncanplaythrough event?
It runs JavaScript when media can play through without stopping. In JavaScript the event is named canplaythrough.
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 oncanplaythrough attribute or addEventListener?
Prefer addEventListener('canplaythrough', …) in JavaScript. The inline oncanplaythrough attribute works but mixes behavior into the markup and allows only one handler per element.
oncanplay onchange