What is it Middleware (middleware)? Whose middleware it?
First we need to understand the request and response,
We request that the client sends a request to the server,
Is the response, the server returns the data to the client according to the client's request,
So middleware, is that when a client requests the server, some data will be transmitted to the server, then the middleware is to deal with these clients to send data to the server side, if there are a good number of middleware services, then when the client to the server when sending a request, we will first go through all of the middleware in turn executed, and then send the request to the server. This is the role of middleware;