Instruction: Define middleware in the context of Express.js and its use cases.
Context: This question evaluates the candidate's understanding of middleware functions in Express.js, which are crucial for handling HTTP requests.
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Middleware functions can perform a wide array of tasks such as executing code, making changes to the request and the response objects, ending the request-response cycle, and calling the next middleware function in the stack. If the current middleware does not end the request-response cycle, it must call next() to pass control to the next middleware function. Otherwise, the request will be left hanging.
The use cases for middleware in Express.js are vast and varied. They include, but are not limited to, logging requests to the console for debugging purposes, parsing JSON bodies...