QGIS2web Openlayers map export as PNG

Followig the query here:

QGIS2web Export open layers map as PDF, PNG or JPEG

I would like to be able to export my map in the PNG format.

Unfortunately the code from here:

https://www.kreidefossilien.de/webgis/dokumentation/beispiele/export-als-png-hoehere-aufloesung

doesn’t work

I embedded this code into the file, which has been uploaded here:

https://jsfiddle.net/x6wgz12v/

The console throws:

Uncaught ReferenceError: $ is not defined

where an answer is here:

https://stackoverflow.com/questions/2925130/jquery-equivalent-of-getting-the-context-of-a-canvas

but it doesn’t match my code

    var canvas = $('canvas').get(0);

The PNG export button doesn’t work at all

I’ve changed the var canvas to

var canvas = document.getElementById(‘canvas’);

https://competa.com/html5-canvas-the-basics

and now the console shows another problem:

qgis2web.js:871 Uncaught TypeError: Cannot read property ‘width’ of null

indicating the canvas size function:

   function setDPI(canvas, dpi) {
    var scaleFactor = dpi / 96;
    canvas.width = Math.ceil(canvas.width * scaleFactor);
    canvas.height = Math.ceil(canvas.height * scaleFactor);
    var ctx=canvas.getContext("2d");
    ctx.scale(scaleFactor, scaleFactor);
   }

where an answer is here:

https://stackoverflow.com/questions/16509020/uncaught-typeerror-cannot-read-property-width-of-null

but doesn’t match my situation.

The final question is how to get the Openlayers maps generated in QGIS2web plugin downloadable as a PNG format?