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The HTMLCanvasElement.getContext() method returns a drawing context on the canvas, or null if the context identifier is not supported.

Syntax

var ctx = canvas.getContext(contextType);
var ctx = canvas.getContext(contextType, contextAttributes);

Parameters

contextType
Is a DOMString containing the context identifier defining the drawing context associated to the canvas. Possible values are:
  • "2d", leading to the creation of a CanvasRenderingContext2D object representing a two-dimensional rendering context.
  • "webgl" (or "experimental-webgl") which will create a WebGLRenderingContext object representing a three-dimensional rendering context. This context is only available on browsers that implement WebGL version 1 (OpenGL ES 2.0).
  • "webgl2" which will create a WebGL2RenderingContext object representing a three-dimensional rendering context. This context is only available on browsers that implement WebGL version 2 (OpenGL ES 3.0).
  • "bitmaprenderer" which will create an ImageBitmapRenderingContext which only provides functionality to replace the content of the canvas with a given ImageBitmap.

Note: The identifier "experimental-webgl" is used in new implementations of WebGL. These implementations have either not reached test suite conformance, or the graphics drivers on the platform are not yet stable. The Khronos Group certifies WebGL implementations under certain conformance rules.

contextAttributes

You can use several context attributes when creating your rendering context, for example:

const gl = canvas.getContext('webgl', {
  antialias: false,
  depth: false
});
2d context attributes:
  • alpha: Boolean that indicates if the canvas contains an alpha channel. If set to false, the browser now knows that the backdrop is always opaque, which can speed up drawing of transparent content and images.
  • (Gecko only) willReadFrequently: Boolean that indicates whether or not a lot of read-back operations are planned. This will force the use of a software (instead of hardware accelerated) 2D canvas and can save memory when calling getImageData() frequently. This option is only available, if the flag gfx.canvas.willReadFrequently.enable is set to true (which, by default, is only the case for B2G/Firefox OS).
  • (Blink only) storage: String that indicates which storage is used ("persistent" by default).
WebGL context attributes:
  • alpha: Boolean that indicates if the canvas contains an alpha buffer.
  • antialias: Boolean that indicates whether or not to perform anti-aliasing.
  • depth: Boolean that indicates that the drawing buffer has a depth buffer of at least 16 bits.
  • failIfMajorPerformanceCaveat: Boolean that indicates if a context will be created if the system performance is low.
  • powerPreference: A hint to the user agent indicating what configuration of GPU is suitable for the WebGL context. Possible values are:
    • "default": Let the user agent decide which GPU configuration is most suitable. This is the default value.
    • "high-performance": Prioritizes rendering performance over power consumption.
    • "low-power": Prioritizes power saving over rendering performance.
  • premultipliedAlpha: Boolean that indicates that the page compositor will assume the drawing buffer contains colors with pre-multiplied alpha.
  • preserveDrawingBuffer: If the value is true the buffers will not be cleared and will preserve their values until cleared or overwritten by the author.
  • stencil: Boolean that indicates that the drawing buffer has a stencil buffer of at least 8 bits.

Return value

A RenderingContext which is either a

If the contextType doesn't match a possible drawing context, null is returned.

Examples

Given this <canvas> element:

<canvas id="canvas" width="300" height="300"></canvas>

You can get a 2d context of the canvas with the following code:

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
console.log(ctx); // CanvasRenderingContext2D { ... }

Now you have the 2D rendering context for a canvas and you can draw within it.

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'HTMLCanvasElement.getContext' in that specification.
Living Standard No change since the latest snapshot, HTML5
HTML 5.1
The definition of 'HTMLCanvasElement.getContext' in that specification.
Recommendation  
HTML5
The definition of 'HTMLCanvasElement.getContext' in that specification.
Recommendation Snapshot of the HTML Living Standard containing the initial definition.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support YesEdge Full support 12Firefox Full support 3.6IE Full support 9Opera Full support 9Safari Full support 3.1WebView Android Full support YesChrome Android Full support YesEdge Mobile ? Firefox Android Full support 4Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes
WebGL contextChrome Full support 33
Full support 33
Full support 9
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
Edge Full support Yes
Alternate Name
Full support Yes
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
Firefox Full support 24
Full support 24
Full support 3.6
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
IE Full support 11
Alternate Name
Full support 11
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
Opera Full support 15
Full support 15
Full support 9
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
Safari Full support 5.1
Alternate Name
Full support 5.1
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
WebView Android ? Chrome Android ? Edge Mobile Full support YesFirefox Android Full support Yes
Alternate Name
Full support Yes
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl
Opera Android ? Safari iOS ? Samsung Internet Android ?
WebGL2 contextChrome Full support 56Edge No support No
Notes
No support No
Notes
Notes WebGL 2 is under consideration in Edge, with a roadmap priority of medium. See the Edge Platform status for latest information.
Firefox Full support 51
Full support 51
Full support 25
Alternate Name
Alternate Name Uses the non-standard name: experimental-webgl2
IE No support NoOpera No support NoSafari No support NoWebView Android ? Chrome Android No support NoEdge Mobile ? Firefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
2d alpha context attributeChrome Full support 32Edge ? Firefox Full support 30IE No support NoOpera Full support YesSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile ? Firefox Android Full support 30Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
failIfMajorPerformanceCaveat attributeChrome Full support YesEdge ? Firefox Full support 41IE Full support YesOpera Full support YesSafari ? WebView Android No support NoChrome Android No support NoEdge Mobile ? Firefox Android Full support 41Opera Android ? Safari iOS ? Samsung Internet Android No support No
bitmaprenderer contextChrome Full support 56Edge ? Firefox Full support 46IE No support NoOpera Full support 43Safari No support NoWebView Android No support NoChrome Android Full support 56Edge Mobile ? Firefox Android Full support 46Opera Android Full support 43Safari iOS No support NoSamsung Internet Android Full support 6.0
powerPreference attributeChrome No support NoEdge No support NoFirefox Full support 63IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile No support NoFirefox Android Full support 63Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
See implementation notes.
See implementation notes.
Uses a non-standard name.
Uses a non-standard name.

See also

Documentlabels en -medewerkers

Laatst bijgewerkt door: mfluehr,