Add download URL button to Vimm's Vault pages

vimm_download_url.js

// ==UserScript==
// @name         Vimm's Lair Download Button
// @homepage     https://gist.github.com/devwolf75/8ea522aa06aefa22ae1e8cdda810c722
// @version      0.1
// @description  Vimm's Lair script to add a 'Download URL' button on the page, copies URL to clipboard.
// @icon         https://www.google.com/s2/favicons?sz=64&domain=vimm.net
// @author       devwolf75
// @match        https://vimm.net/vault/*
// @include      https://vimm.net/vault/*
// @grant        none
// @require      https://code.jquery.com/jquery-3.6.0.min.js
// @downloadURL  https://gist.githubusercontent.com/devwolf75/8ea522aa06aefa22ae1e8cdda810c722/raw/63a667d2fe1102f94ba886bf0c5749b1b530ee86/vimm_download_url.js
// @updateURL    https://gist.githubusercontent.com/devwolf75/8ea522aa06aefa22ae1e8cdda810c722/raw/63a667d2fe1102f94ba886bf0c5749b1b530ee86/vimm_download_url.js
// ==/UserScript==
var buttonInserted = false;
var mediaId = "";
var url = "";

window.addEventListener("load", function () {
    addButton();
    document.getElementById("disc_number").addEventListener("change", function() {
        removeButton();
        addButton();
    });
});

window.addEventListener("focus", function () {
    addButton();
    document.getElementById("disc_number").addEventListener("change", function() {
        removeButton();
        addButton();
    });
});

function addButton(url) {
    mediaId = document.querySelector("input[name='mediaId']").value;
    url = `https://dl3.vimm.net/?mediaId=${mediaId}`;
    let button = $("#dl_form").append(
        '<button type="button" style="width:100%" id="copy_url">Copy URL</button>'
    );

    button.on("click", function () {
        if (document.hasFocus()) {
            (async () => {
                await navigator.clipboard.writeText(url);
            })();
        }
    });
    buttonInserted=true;
}

function removeButton() {
    let button = document.getElementById("copy_url").remove();
    buttonInserted = false;
}

function clearText() {
    (async () => {
        await navigator.clipboard.writeText(url);
    })();
}