expressjs repo documentation

Question

I want to understand the internal working of Expressjs (just curious). Much of the thing are clear but I am not able to understand the chaining of routing and middleware. How expressjs add all the route and middleware to path / and how it keep the stack of route with middleware internally

So I will be very thankful to you if you provide some documentation or link from where I get the understanding how expressjs work internally

Thanks

Answer 1

ExpressJS is just an HTTP server allowing you to route and manipulate the received requests and returning a response.

So if you carefully look at the HTTP packet format below,

you can find the method and the path in the first line.

So, basically here express-router has a regex matcher that tries to match the HTTP request it receives to the predefined routes declared in the express application.

If you check L:43 Router, here it shows that the route you declare is just a function containing 3 constants:

1. path - That would be a path to match.
2. stack - Following a proper format, the URL is broken down using the / separator and a stack is formed in order of it's parsing, comprising another function called layer.
3. methods - Methods are the HTTP methods that we declare along with the path.

Parsing

So when a request is made, let's suppose: http://localhost:8000/user/1/test

1. We get the path: /user/1/test
2. The router's handle function is executed. Then this path is broken down into layers and formed a stack: ['user', '*', 'test']
3. This stack is then matched with that of the route objects that are pre-declared in the application and are used as Route functional objects.
4. As soon as it finds the match the callback is executed!