skibbl-drawing-downloader.user.js

// ==UserScript==
// @name         Skribbl drawing downloader
// @namespace    https://delivator.me/
// @version      0.4
// @description  Adds a button to skribbl.io to save the drawing
// @author       Delivator
// @match        https://skribbl.io/*
// @grant        none
// @homepage     https://gist.github.com/Delivator/091d7aa72e785782a351fe9bcd7f7e1a
// @icon         https://skribbl.io/res/favicon.png
// ==/UserScript==

(function () {
  'use strict';
  $(document).ready(() => {
    const button = $('<a href="#" download="" id="btnSaveImage" role="button" class="btn btn-info" style="position: fixed; top: 60px; left: 10px;">Save drawing</a>');
    const canvas = document.getElementById("canvasGame");
    const body = $("body");

    body.append(button);
    button.click(() => {
      const filename = "drawing_" + new Date().getTime() + ".png";
      button.attr("href", canvas.toDataURL("image/png"));
      button.attr("download", filename);
    });
  });
})();