Returns a canvas element that contains the result of the map print.
Returns a data URL (i.e. data:...) that contains a PNG image.
Use quality (between 0 and 1, defaults to 0.8) to control the image size / compression.
See also https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL.
Optionalquality: number
The result of a print operation.