javascript - Node : how to implement isLoggedIn before all routes?

Question

我想写一个辅助函数isLoggedIn，用于判断是否有用户登录，如果登录，设置res.locals.is_logged_in = true。

var isLoggedIn = function(req, res, next) {
    User.findById(sessions.user_id, function(err, user) {
        if (err) throw err;
        return !user ? false : true;
    });
};

然后，在所有路由之前，我写

.use(express.static(path.join(__dirname, '/public')))
.use(express.static(path.join(__dirname, '/bower_components')))
.use(flash)
.use(function(req, res, next) {
    if (isLoggedIn(req, res, next)) {
        res.locals.is_logged_in = true;
        res.locals.current_user = '/users/' + req.user._id;
    } else {
        res.locals.is_logged_in = false;
    }

    res.locals.showTests = app.get('env') !== 'production' &&
    req.query.test === '1';

    next();
});

var routes = require('./routes/routes.js');
app.use('/', routes.staticPages());
app.use('/', routes.sessions(sessionHelper));
app.use('/users', routes.users(sessionHelper));

但我意识到 findById 是一个异步函数，所以我无法通过这种方式获得正确的行为。

我试过了

var isLoggedIn = function(callback) {
    User.findById(sessions.user_id, function(err, user) {
        if (err) throw err;
        callback(user);
    });
};

.use(function(req, res, next) {
        sessionHelper.isLoggedIn(function(user) {
            if (!user) {
                console.log("no");
                res.locals.is_logged_in = false;
            } else {
                console.log("yes");
                res.locals.is_logged_in = true;
                res.locals.current_user = '/users/' + req.user._id;
            }
        });

        res.locals.showTests = app.get('env') !== 'production' &&
            req.query.test === '1';

        next();
    });

它也不正确:在某些路由中，我打印res.locals.is_logged_in，得到值"undefined"，如何解决这个问题？

Answer 1

您需要异步调用。在您的情况下，您应该使用回调:

.use(function(req, res, next) {
    sessionHelper.isLoggedIn(function(user) {
        if (!user) {
            console.log("no");
            res.locals.is_logged_in = false;
        } else {
            console.log("yes");
            res.locals.is_logged_in = true;
            res.locals.current_user = '/users/' + req.user._id;
        }

        next(); // next MUST be here in order to continue AFTER db query
    });

    res.locals.showTests = app.get('env') !== 'production' &&
        req.query.test === '1';

    //next(); // remove this from here, as it makes it continue without waiting for db query
});