Convert and extract canvas contents into image

canvas2image.js

/// Convert canvas content into image.
/// Usage: Run this script in console.

/***************************************************************
 *  Warning Notice
 *
 *  This script is provided for EDUCATIONAL PURPOSES ONLY.
 *  Do NOT use this script for illegal or copyright infringement activities.
 *
 *  This script is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  The GNU General Public License can be found at
 *  http://www.gnu.org/copyleft/gpl.html.
 *
 *  This script is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
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// create new window with blank document
var w = window.open("", document.title);

// create new document
var newDoc = document.implementation.createHTMLDocument("New Document");
newDoc.body.style = "margin: 0px; background: #0e0e0e;";
newDoc.title = document.title;

// add front image if found
try {
    var frontimg = document.getElementsByClassName('front-link-page')[0].querySelectorAll('img')[0];
    frontimg.style = "display: block;margin: auto;";
    newDoc.body.appendChild(frontimg);
}
catch {
	console.log("front-link-page not found");
}

// get every canvas then convert into array to use forEach
var canvasimgs = document.getElementsByTagName('canvas');
Array.from(canvasimgs).forEach(
    function(currentValue, currentIndex) {
        
        // prevent exception if canvas is blank
        try {
            // create new img element
            var img = newDoc.createElement("img");
            img.src = currentValue.toDataURL('image/png');
            img.style = "display: block;margin: auto;";
            img.id = "id" + currentIndex;

            // attach img to the document
            newDoc.body.appendChild(img);
        } catch {
            return;
        }

    });

// swap document contents
w.document.replaceChild(
    w.document.importNode(newDoc.documentElement, true),
    w.document.documentElement
);

please describe your problem.
the script collects 'canvas' tags, then try convert it into images, then returns new html pages with converted.