在Express中，404响应不是错误的结果，因此错误处理程序中间件不会捕获它们。你所需要做的就是在堆栈的最底部(所有其他函数的下面)添加一个中间件函数来处理404响应:

app.use(function (req, res, next) {
// YOU CAN CREATE A CUSTOM EJS FILE TO SHOW CUSTOM ERROR MESSAGE
  res.status(404).render("404.ejs")
})

我认为你应该首先定义你所有的路线，然后作为最后的路线添加

//The 404 Route (ALWAYS Keep this as the last route)
app.get('*', function(req, res){
  res.status(404).send('what???');
});

一个示例应用程序的工作:

app.js:

var express = require('express'),
    app = express.createServer();

app.use(express.static(__dirname + '/public'));

app.get('/', function(req, res){
  res.send('hello world');
});

//The 404 Route (ALWAYS Keep this as the last route)
app.get('*', function(req, res){
  res.send('what???', 404);
});

app.listen(3000, '127.0.0.1');

alfred@alfred-laptop:~/node/stackoverflow/6528876$ mkdir public
alfred@alfred-laptop:~/node/stackoverflow/6528876$ find .
alfred@alfred-laptop:~/node/stackoverflow/6528876$ echo "I don't find a function for that... Anyone knows?" > public/README.txt
alfred@alfred-laptop:~/node/stackoverflow/6528876$ cat public/README.txt 

.
./app.js
./public
./public/README.txt

alfred@alfred-laptop:~/node/stackoverflow/6528876$ curl http://localhost:3000/
hello world
alfred@alfred-laptop:~/node/stackoverflow/6528876$ curl http://localhost:3000/README.txt
I don't find a function for that... Anyone knows?

// Add this middleware
// error handler
app.use(function(err, req, res, next) {
 // set locals, only providing error in development
   res.locals.message = err.message;
   res.locals.error = req.app.get('env') === 'development' ? err : {};

 // render the error page
   res.status(err.status || 500);
   res.render('error');
  });

我发现这个例子很有帮助:

https://github.com/visionmedia/express/blob/master/examples/error-pages/index.js

所以，它实际上是这一部分:

// "app.router" positions our routes
// above the middleware defined below,
// this means that Express will attempt
// to match & call routes _before_ continuing
// on, at which point we assume it's a 404 because
// no route has handled the request.

app.use(app.router);

// Since this is the last non-error-handling
// middleware use()d, we assume 404, as nothing else
// responded.

// $ curl http://localhost:3000/notfound
// $ curl http://localhost:3000/notfound -H "Accept: application/json"
// $ curl http://localhost:3000/notfound -H "Accept: text/plain"

app.use(function(req, res, next) {
  res.status(404);

  // respond with html page
  if (req.accepts('html')) {
    res.render('404', { url: req.url });
    return;
  }

  // respond with json
  if (req.accepts('json')) {
    res.json({ error: 'Not found' });
    return;
  }

  // default to plain-text. send()
  res.type('txt').send('Not found');
});

404页面应该在调用app.listen.Express支持路由路径中的*之前设置。这是一个匹配的特殊字符 任何东西。这可以用来创建一个匹配所有请求的路由处理程序。

app.get('*', (req, res) => {
  res.render('404', {
    title: '404',
    name: 'test',
    errorMessage: 'Page not found.'
  })
})

在app.js的最后一行放入这个函数。这将覆盖默认的page-not-found错误页面:

app.use(function (req, res) {
    res.status(404).render('error');
});

它将覆盖没有有效处理程序的所有请求，并呈现您自己的错误页面。