Stackoverflow Add Button For Copy to clipboard

Stackoverflow add button for copy to clipboard.
Ekde 2022/01/15. Vidu La ĝisdata versio.
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// ==UserScript==

// @namespace    https://greasyfork.org/zh-TW/users/142344-jasn-hr
// @name               Stackoverflow Add Button For Copy to clipboard
// @name:zh-TW         Stackoverflow 增加複製按鈕
// @name:zh-CN         Stackoverflow 添加复制按钮
// @name:ja            Stackoverflow はコピーボタンを追加します
// @description        Stackoverflow add button for copy to clipboard.
// @description:zh-TW  Stackoverflow 增加複製按鈕以複製原始碼到剪貼簿。
// @description:zh-CN  Stackoverflow 添加复制按钮以复制原始码到剪贴簿。
// @description:ja     ソースコードをクリップボードにコピーするためのコピーボタンをStackoverflowに追加しました。
// @copyright    2022, HrJasn (https://greasyfork.org/zh-TW/users/142344-jasn-hr)
// @license      GPL-3.0-or-later
// @version      1.5
// @icon         https://www.google.com/s2/favicons?domain=stackoverflow.com
// @include      /^http[s]?://stackoverflow\.com/questions/[0-9]+/.*/
// @grant        none
// ==/UserScript==

window.onload = function() {

    const precodeObjs = document.querySelectorAll('pre code');

    const scrollbarChange = function(){
        let copyBtn = this.querySelector('input[value="Copy"]');
        copyBtn.style.right = (5-this.scrollLeft) + 'px';
        copyBtn.style.bottom = (5-this.scrollTop) + 'px';
    }

    precodeObjs.forEach(function(precodeObj){
        let copyBtn = document.createElement('input');
        copyBtn.type='button';
        copyBtn.value='Copy';
        copyBtn.style='cursor:pointer;opacity:0;position:absolute;right:5px;bottom:5px;font-size:15px;padding:10px;background-color:#888888;border:0px;border-style:solid;color: #ffffff;text-shadow: 0px 0px 2px #ffffff;border-radius:5px;';
        precodeObj.parentNode.style.position = 'relative';
        precodeObj.parentNode.appendChild(copyBtn);
        precodeObj.parentNode.addEventListener("wheel",scrollbarChange,false);
        precodeObj.parentNode.addEventListener("scroll",scrollbarChange,false);
        precodeObj.parentNode.addEventListener("keydown",scrollbarChange,false);
        copyBtn.addEventListener('click', function(){
            let targetObj = this.parentNode;
            let srcText = targetObj.textContent || targetObj.innerText || targetObj.nodeValue || '';
            navigator.clipboard.writeText(srcText);
            //let clipText = navigator.clipboard.readText();
            console.log(srcText);
            if(srcText !== undefined){
                this.value='Copied';
            }
        });
        copyBtn.addEventListener('mouseenter', function(){
            this.style.opacity = 1;
        });
        copyBtn.addEventListener('mouseleave', function(){
            this.style.opacity = 0;
        });
    });

}