Javascript 节点和Passport处理用户名已存在

我正试图让我的代码处理一个已经存在的用户名。我知道passport是通过console.log（err）自动完成的，但是，如果出现这种情况，我想向用户闪现一条消息，所以我需要添加更多的代码来完成。这似乎是可行的，但是，当我以这种方式实现代码时，我会遇到很多控制台错误，我希望在将来避免任何错误。 这是我的密码：

router.post("/", isLoggedIn, isAdministrator, async function(req, res){ 
    let users = [];
    let newUser = new User({
        username: req.body.user["username"],
        first_name: req.body.user["first_name"],
        middle_name: req.body.user["middle_name"],
        last_name: req.body.user["last_name"],
        email_address: req.body.user["email_address"],
        phone_number: req.body.user["phone_number"],
        street: req.body.user["street"],
        city: req.body.user["city"],
        state: req.body.user["state"],
        zip: req.body.user["zip"],
        user_permissions: req.body.user["user_permissions"],
    });
    try {
        users = await User.find({});
    }
    catch (err) {console.log(err);} 

    users.forEach(function(user) {
        if (user.username == newUser.username){
        // flash username already exists
        console.log("User Already Exists")
        return res.redirect("/users/add");
        }
    });
// If username does not exist
    try {
        await User.register(newUser, req.body.user["password"]);
    }
    catch (err) {console.log(err);} 

    res.redirect("/users");
});

下面是控制台正在记录的内容

User Already Exists
ctor [UserExistsError]: A user with the given username is already registered
    at ...\node_modules\passport-local-mongoose\index.js:237:17
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at async ...\routes\users.js:93:3
(node:4780) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:518:11)
    at ServerResponse.header (...\node_modules\express\lib\response.js:771:10)
    at ServerResponse.location (...\node_modules\express\lib\response.js:888:15)
    at ServerResponse.redirect (...\node_modules\express\lib\response.js:926:18)
    at ...\routes\users.js:97:6
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
(node:4780) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:4780) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

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正如我所说，这段代码的逻辑仍然运行良好，但我担心代码中的承诺拒绝部分。似乎它仍在尝试处理最后一行中的最后一个res.redirect（“/users”），尽管我之前已经返回了res.redirect。这有什么原因吗？我应该担心吗？如果用户名已经存在，使用passport实现flash有更好的方法吗？谢谢。

这不是你问题的答案，但我觉得有必要提一下：

users.forEach(function(user) {
   if (user.username == newUser.username){
    // flash username already exists
    console.log("User Already Exists")
    return res.redirect("/users/add");
   }
});

与其执行上述操作，不如让DB系统为您执行，而不是遍历内存中的用户列表？ 像这样：

---

实际上，这不仅有助于清理我的代码，而且还解决了我的问题；我不再收到实现此代码的错误消息。非常感谢你，我真不敢相信我竟然没有想过用这种方式来做，这样会更好。

users = await User.find({ username: { $eq: newUser.username }});