ReferenceError：未定义Gmail

Question

我尝试使用gmail.js来获取当前用户的电子邮件，以便可以将其与popup.js中用于登录的电子邮件一起检查。我需要尽快从当前打开的gmail中获取当前用户的电子邮件，因此我可以将其存储在存储中，然后从那里检查登录提供的电子邮件是否与该gmail的电子邮件匹配。但是，我遇到Error in event handler for tabs.onUpdated: ReferenceError: Gmail is not defined问题。

我该如何解决？

这是我的文件

{
    "page_action": {
        "default_title": "Browser Extension",
        "default_popup": "index.html"
    },
    "background": {
        "scripts": ["extension/js/background.js"],
        "persistent": true
    },
    "options_page": "index.html",
    "content_scripts": [
        {
            "matches": [
                "https://mail.google.com/mail/*/*",
                "http://mail.google.com/mail/*/*"
            ],
            "js": [
                "extension/js/jquery.min.js",
                "extension/js/gmail.js",
                "extension/js/content.js"
            ],
            "css": ["extension/css/main.css"],
            "run_at": "document_end"
        }
    ],
    "permissions": [
        "contextMenus",
        "tabs",
        "storage",
        "webNavigation",
        "notifications",
        "cookies",
        "identity",
        "identity.email",
        "*://mail.google.com/mail/*/*",
    ],
}


background.js

function check(tabId, changeInfo, tab) {
    const filter = [
        'https://mail.google.com/',
        'http://mail.google.com/',
        'https://inbox.google.com/'
    ];
  if (changeInfo.status !== undefined && changeInfo.status === 'complete') {
        console.log('completed');
        var gmail = new Gmail(); // I get error here 
        console.log('Hello from background', gmail.get.user_email());
    }
    filter.forEach(item => {
        if (tab.url.indexOf(item) >= 0) {
            chrome.pageAction.show(tabId);
        }
    });
}

chrome.tabs.onUpdated.addListener(check);

如果我改为在内容脚本中使用，则无法定义。

content.js

const main = function() {
    // NOTE: Always use the latest version of gmail.js from
    // https://github.com/KartikTalwar/gmail.js
    var j = document.createElement('script');
    j.src = chrome.extension.getURL('jquery.min.js');
    console.log('j', j);
    (document.head || document.documentElement).appendChild(j);

    var g = document.createElement('script');
    g.src = chrome.extension.getURL('gmail.js');
    (document.head || document.documentElement).appendChild(g);
    console.log('main');
    const gmail = new Gmail();
    console.log('Hello,', gmail.get.user_email()); // undefined
};

refresh(main);