# OffscreenCanvas >![](../../public_sys-resources/icon-note.gif) **NOTE:** >The APIs of this module are supported since API version 7. Defines a canvas object that can be rendered off the screen. ## Attributes

Name	Type	Description
width	number	Width of the offscreen canvas object.
height	number	Height of the offscreen canvas object.

## Methods

Name	Parameter	Description
getContext	contextId: "2d", options?: CanvasRenderingContext2DSettings	The invoking methods are as follows: var ctx = canvas.getContext(contextId); var ctx = canvas.getContext(contextId, options); The contextId parameter is mandatory. Currently, only the value 2d is supported. The options parameter is optional and is not supported currently. Obtains the context for drawing on an offscreen canvas. The parameter can be set only to 2d. The return value is a 2D drawing object that provides specific 2D drawing operations. For details, see OffscreenCanvasRenderingContext2D.
toDataURL	type?: string, quality?: number	Generates a URL containing image display information. type: specifies the image format. This parameter is optional. The default value is image/png. quality: specifies the image quality, which ranges from 0 to 1 when the image format is image/jpeg or image/webp. If the value of this parameter exceeds the value range, the default value 0.92 will be used.
transferToImageBitmap	None	Creates an ImageBitmap object from the most recent image rendered by Offscreen Canvas.

Name

Parameter

Description

getContext

contextId: "2d", options?: CanvasRenderingContext2DSettings

The invoking methods are as follows:

var ctx = canvas.getContext(contextId);

var ctx = canvas.getContext(contextId, options);

The contextId parameter is mandatory. Currently, only the value 2d is supported. The options parameter is optional and is not supported currently.

Obtains the context for drawing on an offscreen canvas. The parameter can be set only to 2d. The return value is a 2D drawing object that provides specific 2D drawing operations. For details, see OffscreenCanvasRenderingContext2D.

toDataURL

type?: string, quality?: number

Generates a URL containing image display information.

type: specifies the image format. This parameter is optional. The default value is image/png.
quality: specifies the image quality, which ranges from 0 to 1 when the image format is image/jpeg or image/webp. If the value of this parameter exceeds the value range, the default value 0.92 will be used.

transferToImageBitmap

None

Creates an ImageBitmap object from the most recent image rendered by Offscreen Canvas.

## Example ``` var canvas = this.$refs.canvasId.getContext('2d'); var offscreen = new OffscreenCanvas(500,500); var offscreenCanvasCtx = offscreen.getContext("2d"); // ... some drawing for the canvas using the offscreenCanvasCtx ... var dataURL = offscreen.toDataURL(); console.log(dataURL); //data:image/png;base64,xxxxxx var bitmap = offscreen.transferToImageBitmap(); canvas.transferFromImageBitmap(bitmap); ```