Express 中间件被多次调用

Question

app.use(function(req, res, next) {
    var chatlog = [];
    console.log('executed many timews why?')   
 var chatlog = redisClient.lrange('messages', 0, 99, function(err, reply) {
        if (!err) {
            var result = [];
            for (var msg in reply) result.push(JSON.parse(reply[msg]));
            if (result.length == 0) { 
                result.push({
                    "msg": 'welcome',
                    "nickname": "guest1"
                })
            }
            console.log(result)
        } else {
            console.log('error getting chat messages')
        }
        res.locals = {
            chatlog: result
        };
        next();
        return
    });

  app.get('/', (req, res) => {
 res.render('index', {     })
  })

当我访问 '/' 一次时，控制台会打印以下内容：

executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]
executed many timews why
executed many timews why
executed many timews why
executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
executed many timews why
executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]
[ { msg: 'welcome', nickname: 'guest1' } ]
executed many timews why
[ { msg: 'welcome', nickname: 'guest1' } ]

如何让我的中间件只执行一次？如果我拿走next，它只运行一次但页面不会加载，如果我保留next()，它会执行很多次。

Answer 1

您的中间件已设置为针对每个请求进行调用。这意味着如果 Express 配置不正确，它将为您碰巧在索引模板中使用的每个图像、样式表或 JS 文件调用。

如果这些文件由express.static 提供，请确保在express.static 声明之后加载您的中间件：

app.use(express.static(...));

app.use(...your middleware...);

app.get('/', ...);

这样，您的中间件将不会被调用以获取静态资源，因为express.static 将在您的中间件之前处理它们。

您也可以创建一个单独的中间件函数并将其插入到特定的路由中：

let myMiddleware = function(req, res, next) {
  ...
});

app.get('/', myMiddleware, function(req, res) {
  res.render('index', {})
});