Instruction: Describe middleware's role in Node.js applications outside the context of Express.js.
Context: This question tests the candidate's understanding of the middleware pattern as a generic concept in Node.js applications, not limited to Express.js.
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At its core, middleware is fundamentally a function with access to the request and response objects, and the next middleware function in the application’s request-response cycle. This allows middleware functions to execute code, make changes to the request and response objects, end the request-response cycle, or call the next middleware function in the stack. While Express.js popularized this pattern in the Node.js ecosystem, the concept of middleware transcends it and can be implemented in any Node.js application, regardless of the framework or library used.
For instance, in raw Node.js applications without Express.js, middleware can be implemented to handle various tasks such as logging, authentication, and data validation. Such...