在带有express和connect的节点中使用中间件的最常见方法是什么

Question

Thinking about the correct way, how to make use of middlewares in a node.js web project using express and connect which is growing up at the moment.

Of course there are middlewares right now wich has to pass or extend requests globally but in a lot of cases there are special jobs like prepare incoming data and in this case the middleware would only work for a set of http-methods and routes.

I've a component based architecture and each component brings it's own middleware layer which can implement those for requests this component can handle. On app startup any required component is loaded and prepared. Is it a good idea to bind the middleware code execution to URLs to keep cpu load lower or is it better to use middlewares only for global purposes?

Here's some dummy how an url related middleware look like.

app.use(function(req, res, next) {            

        // Check if requested route is a part of the current component
        // or if the middleware should be passed on any request
        if (APP.controller.groups.Component.isExpectedRoute(req) ||
            APP.controller.groups.Component.getConfig().MIDDLEWARE_PASS_ALL === true) {
                // Execute the midleware code here
                console.log('This is a route which should be afected by middleware');
                ...
                next();                    
            }else{
                next();
            }
        });

Answer 1

It depends on your setup, but you can be creative.

Say that you want to run a certain middleware for GET requests with a /foo prefix. In that case, you can limit the number of calls to that middleware using something like this:

// matches '/foo', '/foo/bar', '/foo/bar/blah', ...
app.get('/foo*', YourMiddleware);

(replace app.get with app.all to pass all request methods through the middleware, etc.)

If you want to run the middleware only a limited number (one or two) specific routes, you can inject it in the route declaration:

app.get('/bar', YourMiddleware, function(req, res) {
  ...
});

If you have specific sets of middlewares, you can create arrays of them which you can use similarly:

var MiddlewareSet = [ MiddlewareA, MiddlewareB, MiddlewareC ];
...
app.get('/', MiddlewareSet, function(req, res) {
  ...
});

Answer 2

This is like probability. Let us assume, there is 10 urls and your middleware is going to be execute for 7 or 8 urls. Then the better idea is, use your middleware global or otherwise use them as normal function.

Of course, you can do it either way. Hopefully there is no big performance variation, because there is some reasons you have to think about,

1. Unlike PHP, Node.Js application read all of your code store them it in memory when app start. So there is no run-time inclusion of code.

2. Any way you have to stop block execution by using some function(middleware function). The function may do actual operation or check whether the url is eligible to execute actual operation or not(like the code in your post)

Note: Whatever it is, your code should be readable and meaningful and intended to complete operation

Note***: More important you can not avoid cpu load "Javascript/Node.JS". However you can manage it by keep all your variable in local scope as much as possible. So that, the inbuilt garbage collector do the same for you effectively.