Chrome扩展开发：从DOM中选中textarea遇到问题求助

问题背景 #

我已大量查阅textarea选中相关技术资料，但未找到合适的解决方案。

开发目标 #

我正在开发一款Chrome扩展，已成功访问页面DOM，但无法单独选中textarea元素，希望实现指定的选中效果（对应图示功能）。

相关代码文件 #

manifest.json #

{"manifest_version": 2,"name": "DOM","version": "0.0", "background": {"persistent": false,"scripts": ["background.js"]},"content_scripts": [{"matches": ["*://*.stackoverflow.com/*"],"js": ["content.js"]}],"browser_action": {"default_title": "DOM","default_popup": "index.html"},"permissions": ["activeTab","tabs","<all_urls>"]}

index.html #

<!DOCTYPE html>
 <html>

 <head>Fayzan</head>

  <body> <button id="test">DOM!</button>
     <script src="test.js"></script>
  </body>
 </html>

Content.js #

// Listen for messages 
chrome.runtime.onMessage.addListener(function (msg, sender, sendResponse) {
// If the received message has the expected format...    
if (msg.text === 'report_back') {
    // Call the specified callback, passing     
    // the web-page's DOM content as argument    
    sendResponse(document.all[0].outerHTML);
   }
 }); 

background.js #

var urlRegex = /^https?:\/\/(?:[^./?#]+\.)?stackoverflow\.com/;

function doStuffWithDom(domContent) {
    console.log('I received the following DOM content:\n' + domContent);
} // When the browser-action button is clicked... 
chrome.browserAction.onClicked.addListener(function(tab) { // ...check the URL of the active tab against our pattern and...    
    if (urlRegex.test(tab.url)) { // ...if it matches, send a message specifying a callback too        
        chrome.tabs.sendMessage(tab.id, {
            text: 'report_back'
        }, doStuffWithDom);
    }
});

test.js #

document.getElementById("test").addEventListener('click', () => {
    alert("DOM POPUP");
    function modifyDOM() {
        console.log('Tab script:');
        console.log(document.body);
        return document.body.innerHTML;
    }
    chrome.tabs.executeScript({
        code: '(' + modifyDOM + ')();'
    },
        (results) => {
            console.log("fayzan bhatti");
            console.log(results);
        }
    );

});

内容的提问来源于stack exchange，提问作者OnlyCOde