OffscreenCanvas: contextlost event

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The contextlost event of the OffscreenCanvas interface is fired if the browser detects that the OffscreenCanvasRenderingContext2D context is lost. Contexts can be lost for several reasons, such as an associated GPU driver crashes, or the application runs out of memory, and so on.

By default the user agent will attempt to restore the context and then fire the contextrestored event. User code can prevent the context from being restored by calling Event.preventDefault() during event handling.

Syntax

Use the event name in methods like addEventListener(), or set an event handler property.

js
addEventListener("contextlost", (event) => {});

oncontextlost = (event) => {};

Event type

A generic Event.

Examples

The code fragment below detects the contextlost event.

js
const canvas = new OffscreenCanvas(256, 256);
const gl = offscreen.getContext("2d");

// Do drawing etc

canvas.addEventListener("contextlost", (event) => {
  console.log(event);
});

To prevent the context from being restored the event handler code might instead look like this:

js
canvas.addEventListener("contextlost", (event) => {
  event.preventDefault();
});

Specifications

Specification
HTML Standard
# event-contextlost
HTML Standard
# handler-offscreencanvas-oncontextlost

Browser compatibility

BCD tables only load in the browser

See also