canvg canvas getting slower with each edit/ memory usage increase

I have developed a scientific application to measure the area of shapes drawn on a scanned paper using canvg (version 3. something). The application works mostly fine (in Chrome), but gets really slow after a lot of small areas are selected.

var s = canvg('canvas', inp_xmls, {ignoreMouse: true, ignoreAnimation: true});

Each click inside an area performs a bucket fill using the canvg bucket-fill:

var bucket = Bucket(canvas, cfg, event, color);

Subsequently, the image is updated to view the new filled area:

    var lowerimg = svg.image(can.toDataURL());
    console.log(lowerimg)

    lowerimg.node.onload = function () {
        drawDown();

…

function drawDown() {
    inp_xmls = XMLS.serializeToString(svg.node);
    s.loadXml(ctx, inp_xmls);
    s.stop();
}

function undo() {
    var last = svg.last();

    if(svg.index(last) > 1) {
        last.remove();
        drawDown();
        s.draw();
    }
    undoAddArea();
}

Using the memory snapshots I can see ‘strings’ are increasing in size significantly (and image + #document).

The application is available online here:
https://limo.mni.thm.de/
Clicking on “Beispiel” on the right open an example slide in the drawing board.

My questions:

• How can I reduce memory usage of the filling/ drawing on the canvas? Is there a function in canvg to ‘clear’ older layers?
• I need the possibility to ‘undo’ clicks, so I need to store some of them. How do I access the old images like in the ‘undo’ function to remove everything older than 5 edits for example?