express.js中间件说明详解

app.use(function frontControllerMiddlewareExecuted(req, res, next){
console.log('(1) this frontControllerMiddlewareExecuted is executed');
next();
});

app.all('*', function(req, res, next){
console.log('(2) route middleware for all method and path pattern "*", executed first and can do stuff before going next');
next();
});

app.all('/hello', function(req, res, next){
console.log('(3) route middleware for all method and path pattern "/hello", executed second and can do stuff before going next');
next();
});

app.use(function frontControllerMiddlewareNotExecuted(req, res, next){
console.log('(4) this frontControllerMiddlewareNotExecuted is not executed');
next();
});

app.get('/hello', function(req, res){
console.log('(5) route middleware for method GET and path patter "/hello", executed last and I do my stuff sending response');
res.send('Hello World');
});

app.listen(80);

现在我们看到了app.use()方法的唯一性以及它用于声明中间件的原因。

让我们重写我们的示例站点代码：

var app = require("express")();
function checkLogin(){
  return false;
}
function logRequest(){
  console.log("New request");
}
app.use(function(req, res, next){
  logRequest();
  next();
})
app.use(function(req, res, next){
  if(checkLogin()){
    next();
  }
  else{
    res.send("You are not logged in!!!");
  }
})
app.get("/dashboard", function(req, res, next){
  res.send("This is the dashboard page");
});
app.get("/profile", function(req, res, next){
  res.send("This is the dashboard page");
});
app.listen(8080);