marstoy.js

// ==UserScript==
// @name         Add LEGO Hyperlink to MOC Kit Header
// @namespace    http://tampermonkey.net/
// @version      1.4
// @description  Adds a LEGO hyperlink in smaller text on the next line after "MOC MXXXXX Parts Kit" within the specified header, linking to the corresponding LEGO product page.
// @author       Emmet
// @match        *://www.marstoy.net/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // Function to reverse a string
    function reverseString(str) {
        return str.split('').reverse().join('');
    }

    // Target the specific <h1> element
    let header = document.querySelector('h1.product-info__header_title.dj_skin_product_title');

    if (header) {
        let regex = /MOC M(\d{5}) Parts Kit/;
        let match = header.innerHTML.match(regex);

        if (match) {
            let mocNumber = match[1];
            let reversedNumber = reverseString(mocNumber);
            let legoUrl = `https://www.lego.com/en-us/product/${reversedNumber}`;

            // Create a new anchor (link) element
            let link = document.createElement('a');
            link.href = legoUrl;
            link.innerHTML = 'Open product on Lego.com';
            link.style.display = 'block'; // Ensures the link is on the next line
            link.style.fontSize = 'smaller'; // Make the text smaller
            link.style.marginTop = '5px'; // Add some spacing
            link.target = '_blank'; // Open link in a new tab

            // Append the link after the matched text
            header.innerHTML = `MOC M${mocNumber} Parts Kit`;
            header.appendChild(link);
        }
    }
})();