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web api event

HTMLCanvasElement: contextlost event

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The contextlost event of the Canvas API is fired if the user agent detects that the backing storage associated with a CanvasRenderingContext2D context is lost. Contexts can be lost for several reasons like driver crashes or the application runs out of memory, etc.

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.

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

oncontextlost = (event) => { }

Event type

A generic Event.

Example

The code fragment below detects the contextlost event.

const canvas = document.getElementById("canvas");

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

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

const canvas = document.getElementById("canvas");

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

Specifications

SpecificationsStandards references are available on the canonical MDN page.

Browser compatibility

Browser compatibilityCompatibility data is available on the canonical MDN page.

See also