Chess.com problem to Lichess goto

chess.com-problem-to-lichess.user.js

// ==UserScript==
// @name         Chess.com problem to Lichess goto
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Analyse chess.com puzzle with lichess
// @author       You
// @match        *://*.chess.com/puzzles/problem/*
// @run-at       document-end
// @icon         https://www.google.com/s2/favicons?domain=tampermonkey.net
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    function getFEN() {
        const el = document.querySelector('[property="og:image"]');
        return /fen=([a-zA-Z\d\/]+)/.exec(el.content)[1];
    }

    function openLichessAnalysis(fen) {
        window.open(`https://lichess.org/analysis/standard/${fen}`);
    }

    function addButton() {
        const btn = document.createElement('div');

        btn.className = 'icon-font-chess chess-pawn-square play-action-tray-icon';

        btn.onclick = () => {
            openLichessAnalysis(getFEN());
        }

        document.querySelector('.play-action-tray-left').appendChild(btn);
    }

    addButton();
})();