Web/API/HTMLCanvasElement/getContext

The HTMLCanvasElement.getContext() method returns a drawing context on the canvas, or null if the context identifier is not supported, or the canvas has already been set to a different context mode.

Later calls to this method on the same canvas element, with the same contextType argument, will always return the same drawing context instance as was returned the first time the method was invoked. It is not possible to get a different drawing context object on a given canvas element.

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.
desynchronized: Boolean that hints the user agent to reduce the latency by desynchronizing the canvas paint cycle from the event loop
' (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.
desynchronized: Boolean that hints the user agent to reduce the latency by desynchronizing the canvas paint cycle from the event loop
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 or if no hardware GPU is available.
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

CanvasRenderingContext2D for "2d",
WebGLRenderingContext for "webgl" and "experimental-webgl",
WebGL2RenderingContext for "webgl2" or
ImageBitmapRenderingContext for "bitmaprenderer".

If the contextType doesn't match a possible drawing context, or differs from the first contextType requested, 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 StandardThe definition of 'HTMLCanvasElement.getContext' in that specification.	Living Standard	No change since the latest snapshot, HTML5
HTML 5.1The definition of 'HTMLCanvasElement.getContext' in that specification.	Recommendation
HTML5The 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

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`getContext`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1.5	IE Full support 9	Opera Full support 9	Safari Full support 2	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0
bitmaprenderer context	Chrome Full support 56	Edge Full support ≤79	Firefox Full support 46	IE No support No	Opera Full support 43	Safari No support No	WebView Android No support No	Chrome Android Full support 56	Firefox Android Full support 46	Opera Android Full support 43	Safari iOS No support No	Samsung Internet Android Full support 6.0
`desynchronized` attribute	Chrome Full support 81 Notes' Full support 81 Notes' Notes' ChromeOS and Windows Full support 75 Notes' Notes' ChromeOS only Full support 71 Alternate Name' Alternate Name' Uses the non-standard name: `lowLatency`	Edge No support No	Firefox No support No	IE No support No	Opera No support No	Safari No support No	WebView Android No support No	Chrome Android No support No	Firefox Android No support No	Opera Android No support No	Safari iOS No support No	Samsung Internet Android No support No
failIfMajorPerformanceCaveat attribute	Chrome Full support Yes	Edge Full support 12	Firefox Full support 41	IE Full support Yes	Opera Full support Yes	Safari ?	WebView Android No support No	Chrome Android No support No	Firefox Android Full support 41	Opera Android ?	Safari iOS ?	Samsung Internet Android No support No
`powerPreference` attribute	Chrome No support No	Edge No support No	Firefox Full support 63	IE No support No	Opera No support No	Safari No support No	WebView Android No support No	Chrome Android No support No	Firefox Android Full support 63	Opera Android No support No	Safari iOS No support No	Samsung Internet Android No support No
WebGL context	Chrome Full support 33 Full support 33 Full support 9 Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl`	Edge Full support 79 Full support 79 Full support 12 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 Full support 37 Full support 37 Full support 37 Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl`	Chrome Android Full support 33 Full support 33 Full support 18 Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl`	Firefox Android Full support Yes Alternate Name' Full support Yes Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl`	Opera Android Full support 14 Full support 14 Full support 10.1 Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl`	Safari iOS ?	Samsung Internet Android Full support 2.0 Full support 2.0 Full support 1.0 Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl`
WebGL2 context	Chrome Full support 56	Edge Full support 79	Firefox Full support 51 Full support 51 Full support 25 Alternate Name' Alternate Name' Uses the non-standard name: `experimental-webgl2`	IE No support No	Opera No support No	Safari No support No	WebView Android Full support 56	Chrome Android No support No	Firefox Android No support No	Opera Android No support No	Safari iOS No support No	Samsung Internet Android No support No
2d alpha context attribute	Chrome Full support 32	Edge Full support ≤79	Firefox Full support 30	IE No support No	Opera Full support Yes	Safari No support No	WebView Android No support No	Chrome Android No support No	Firefox Android Full support 30	Opera Android No support No	Safari iOS No support No	Samsung 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.