我正在構(gòu)建一個(gè)擴(kuò)展程序，允許您通過(guò) contextMenu 在谷歌新聞中搜索所選文本，但所選文本未顯示在我的查詢中。我錯(cuò)過(guò)了什么？背景.js//creates a context menu When selection is madecontextMenus.createSelectText = chrome.contextMenus.create(    {"title":"Search for '%s'",    "contexts": ["selection"],    "id": "selectedtext"    });var searchURL = 'https://news.google.com/search?q=' + window.getSelection().toString();function searchGoogleForString(url) {    chrome.tabs.create({url: searchURL});}chrome.contextMenus.onClicked.addListener(onRequest);function onRequest(info, tab) {    console.log("User clicked Context Menu Search for " + "selectedtext");    searchGoogleForString(tab["url"]);}清單文件.json{  "name": "Find in Da News",  "description": "Find a similar article",  "version": "0.1.1",  "permissions": [    "contextMenus",    "tabs",    "activeTab"  ],  "background": {    "scripts": ["scripts/background.js"],    "persistent": true  },  "manifest_version": 2,  "icons": {    "48": "squatch.png",    "128": "squatch.png"  },  "browser_action": {    "default_icon": "squatch.png",    "default_popup": "popup.html"  }}謝謝 ：）