Returns a drawing context on the canvas, or null if the context ID is not supported. A drawing context lets you draw on the canvas. The currently accepted values are "2d" and "experimental-webgl". The "experimental-webgl" context is only available on browsers that implement WebGL. Calling getContext with "2d" returns a CanvasRenderingContext2D Object, whereas calling it with "experimental-webgl" returns a WebGLRenderingContext Object.

Object getContext(String contextId);

Returns a data: URL containing a representation of the image in the format specified by type (defaults to PNG).

• If the height or width of the canvas is 0, "data:," representing the empty string, is returned.
• If the type requested is not image/png, and the returned value starts with data:image/png, then the requested type is not supported.
• Chrome supports the image/webp type.
• If the requested type is image/jpeg or image/webp, then the second argument, if it is between 0.0 and 1.0, is treated as indicating image quality; if the second argument is anything else, the default value for image quality is used. Other arguments are ignored.

String toDataURL(String type);