HTML
Living Standard — Last Updated 17 October 2025
Living Standard — Last Updated 17 October 2025
canvas elementPath2D objectsImageBitmap rendering contextOffscreenCanvas interfacecanvas elementscanvas elementSupport in all current engines.
Support in all current engines.
a elements, img elements with
usemap attributes, button elements,
input elements whose type attribute are in
the Checkbox or Radio Button states, input elements that are
buttons, and select elements with a multiple attribute or a display size greater than 1.width — Horizontal dimension
height — Vertical dimension
typedef (CanvasRenderingContext2D or ImageBitmapRenderingContext or WebGLRenderingContext or WebGL2RenderingContext or GPUCanvasContext ) RenderingContext ;
[Exposed =Window ]
interface HTMLCanvasElement : HTMLElement {
[HTMLConstructor ] constructor ();
[CEReactions ] attribute unsigned long width ;
[CEReactions ] attribute unsigned long height ;
RenderingContext ? getContext (DOMString contextId , optional any options = null );
USVString toDataURL (optional DOMString type = "image/png", optional any quality );
undefined toBlob (BlobCallback _callback , optional DOMString type = "image/png", optional any quality );
OffscreenCanvas transferControlToOffscreen ();
};
callback BlobCallback = undefined (Blob ? blob );The canvas element provides scripts with a resolution-dependent bitmap canvas,
which can be used for rendering graphs, game graphics, art, or other visual images on the fly.
Authors should not use the canvas element in a document when a more suitable
element is available. For example, it is inappropriate to use a canvas element to
render a page heading: if the desired presentation of the heading is graphically intense, it
should be marked up using appropriate elements (typically h1) and then styled using
CSS and supporting technologies such as shadow trees.
When authors use the canvas element, they must also provide content that, when
presented to the user, conveys essentially the same function or purpose as the
canvas's bitmap. This content may be placed as content of the canvas
element. The contents of the canvas element, if any, are the element's fallback
content.
In interactive visual media, if scripting is enabled for
the canvas element, and if support for canvas elements has been enabled,
then the canvas element represents embedded content
consisting of a dynamically created image, the element's bitmap.
In non-interactive, static, visual media, if the canvas element has been
previously associated with a rendering context (e.g. if the page was viewed in an interactive
visual medium and is now being printed, or if some script that ran during the page layout process
painted on the element), then the canvas element represents
embedded content with the element's current bitmap and size. Otherwise, the element
represents its fallback content instead.
In non-visual media, and in visual media if scripting is
disabled for the canvas element or if support for canvas elements
has been disabled, the canvas element represents its fallback
content instead.
When a canvas element represents embedded content, the
user can still focus descendants of the canvas element (in the fallback
content). When an element is focused, it is the target of keyboard interaction
events (even though the element itself is not visible). This allows authors to make an interactive
canvas keyboard-accessible: authors should have a one-to-one mapping of interactive regions to focusable areas in the fallback content. (Focus has no
effect on mouse interaction events.) [UIEVENTS]
An element whose nearest canvas element ancestor is being rendered
and represents embedded content is an element that is being used as
relevant canvas fallback content.
The canvas element has two attributes to control the size of the element's bitmap:
width and height. These attributes,
when specified, must have values that are valid
non-negative integers. The rules for parsing non-negative
integers must be used to obtain their numeric
values. If an attribute is missing, or if parsing its value returns an error, then the
default value must be used instead. The width
attribute defaults to 300, and the height attribute
defaults to 150.
When setting the value of the width or height attribute, if the context mode of the canvas
element is set to placeholder, the
user agent must throw an "InvalidStateError" DOMException
and leave the attribute's value unchanged.
The natural dimensions of the canvas element when it
represents embedded content are equal to the dimensions of the
element's bitmap.
The user agent must use a square pixel density consisting of one pixel of image data per
coordinate space unit for the bitmaps of a canvas and its rendering contexts.
A canvas element can be sized arbitrarily by a style sheet, its
bitmap is then subject to the 'object-fit' CSS property.
The bitmaps of canvas elements, the bitmaps of ImageBitmap objects,
as well as some of the bitmaps of rendering contexts, such as those described in the sections on
the CanvasRenderingContext2D, OffscreenCanvasRenderingContext2D, and
ImageBitmapRenderingContext objects below, have an origin-clean flag, which can be set to true or false.
Initially, when the canvas element or ImageBitmap object is created, its
bitmap's origin-clean flag must be set to
true.
A canvas element can have a rendering context bound to it. Initially, it does not
have a bound rendering context. To keep track of whether it has a rendering context or not, and
what kind of rendering context it is, a canvas also has a canvas context mode, which is initially none but can be changed to either placeholder, 2d, bitmaprenderer, webgl, webgl2, or webgpu by algorithms defined in this specification.
When its canvas context mode is none, a canvas element has no rendering context,
and its bitmap must be transparent black with a natural width equal
to the numeric value of the element's width attribute and a natural height equal to
the numeric value of the element's height attribute, those values being interpreted in CSS pixels, and being updated as the attributes are set, changed, or
removed.
When its canvas context mode is placeholder, a canvas element has no
rendering context. It serves as a placeholder for an OffscreenCanvas object, and
the content of the canvas element is updated by the OffscreenCanvas
object's rendering context.
When a canvas element represents embedded content, it provides a
paint source whose width is the element's natural width, whose height
is the element's natural height, and whose appearance is the element's bitmap.
Whenever the width and height content attributes are set, removed, changed, or
redundantly set to the value they already have, then the user agent must perform the action
from the row of the following table that corresponds to the canvas element's context mode.
|
Action | |
|---|---|
|
Follow the steps to set bitmap
dimensions to the numeric values
of the | |
|
Follow the behavior defined in the WebGL specifications. [WEBGL] | |
|
Follow the behavior defined in WebGPU. [WEBGPU] | |
|
If the context's bitmap
mode is set to blank,
run the steps to set an | |
|
Do nothing. | |
|
Do nothing. |
Support in all current engines.
Support in all current engines.
The width
and height
IDL attributes must reflect the respective content attributes of the same name, with
the same defaults.
context = canvas.getContext(contextId [, options ])Support in all current engines.