I've done a little digging into the HTML5 canvas support of the Nintendo 3DS Internet Browser, since it will be used for the 3DSPaint app (as well as others). It seems to be a fairly competent implementation that just was not possible on the Nintendo DSi Browser's limited RAM. NetFront is based on the WebKit layout engine, which was originally used in Apple's Safari browser and later Google's Chrome browser, so there are similarities.

Here is the list of supported functions and properties in the 2D context for developers to reference:

arc
arcTo
beginPath
bezierCurveTo
canvas
clearShadow
clearText
clip
closePath
createImageData
createLinearGradient
createPattern
createRadialGradient
drawImage
drawImageFromRect
fill
fillRect
fillStyle
fillText
font
getImageData
globalAlpha
globalCompositeOperation
isPointInPath
lineCap
lineJoin
lineTo
lineWidth
measureText
miterLimit
moveTo
putImageData
quadraticCurveTo
rect
restore
rotate
save
scale
setAlpha
setCompositionOperation
setFillColor
setLineCap
setLineJoin
setLineWidth
setMiterLimit
setShadow
setStrokeColor
setTransform
shadowBlur
shadowColor
shadowOffsetX
shadowOffsetY
stroke
strokeRect
strokeStyle
strokeText
textAlign
textBaseline
transform
translate

There is a quirk in the Nintendo 3DS implementation of the canvas object. The browser does not seem to refresh it for any procedurally-generated content, such as lines and curves, so something has to be done to the canvas to force a refresh. The simplest method I found was altering a style to it, such as the background color (which you can cover completely with canvas content). I toggle between the color #000 and #111 with the following code:

var toggle=0;

function update_canvas(){
...
...
toggle^=1;
canvas_object.style.backgroundColor = '#' + toggle + toggle + toggle;
}


As I continue to research the canvas implementation, I will try to have more to report. This should at least give a good start for developers.

Here's a quickly hacked together version of the DSiPaint app that works on the Nintendo 3DS Internet Browser. Keep in mind that the final app will be considerably different, as promised in old blogs and BB posts I've made.