What is the function of the Express middleware?
The purpose of Express middleware is to provide functions during the request handling process that can access the request object (req), response object (res), and the next middleware function in the application. Middleware functions can perform various tasks such as validating requests, parsing request bodies, handling errors, and more.
Specifically, middleware functions can be used for:
- Perform request preprocessing: authenticate the request, parse data, validate request parameters, etc., to ensure the validity and security of the request.
- Execute specific tasks during request processing, such as logging, counting request numbers, caching data, etc.
- Error handling: catching and handling exceptions, returning appropriate error responses to improve the robustness of the application.
- Control the request flow: Middleware functions can determine whether to pass the request to the next middleware or route handler based on specific attributes or conditions of the request.
By utilizing different combinations of middleware, it is possible to flexibly build and enhance the functionality of an application. The order in which middleware functions are executed is determined by their registration sequence within the application; each middleware function can choose to pass the request to the next middleware or terminate the request handling process.
