What are middlewares and why is it used in NodeJS? Javascript Interview Series Ep-09

In Node.js, particularly within frameworks like Express.js, middleware refers to a specific type of function that acts as an intermediary between the incoming request and the final response. These functions are essentially building blocks that get executed sequentially, forming a chain or pipeline.
Here's a deeper look at how middleware functions in Node.js:
*Core Function:*
* *Request-Response Manipulation:* Middleware functions have access to three essential arguments:
* `req`: The request object, holding details about the incoming request, like headers, parameters, etc.
* `res`: The response object, used to send responses back to the client.
* `next`: A function that signals the middleware to proceed to the next middleware in the chain or the final route handler.
* *Flexibility in Operations:* Middleware functions can perform various tasks, including:
* Modifying the request and response objects: This can involve tasks like parsing request data, adding headers to the response, or manipulating data before sending it back.
* Executing custom logic: You can perform actions like logging requests, authentication checks, authorization checks, or rate limiting within middleware.
* Sending responses: If certain conditions are met, middleware can entirely terminate the request-response cycle by sending a response directly using the `res` object.
*Order of Execution:*
* *Sequential Processing:* Middleware functions are executed in the order they are registered in the application. This ordered execution allows you to structure your application's logic efficiently.
*Common Use Cases:*
Middleware plays a crucial role in building well-structured and maintainable Node.js applications. Here are some frequent applications of middleware:
* *Logging:* Middleware can be used to log incoming requests and outgoing responses for debugging and monitoring purposes.
* *Authentication and Authorization:* You can implement middleware to check if a user is logged in and has the necessary permissions to access specific resources.
* *Error Handling:* Centralized error handling middleware can ensure consistent error handling across your application.
* *Data Parsing:* Middleware can parse incoming request data (like JSON or form data) and make it readily available for route handlers.
* *Static File Serving:* Middleware can streamline serving static files like images or CSS from a designated directory.
By effectively utilizing middleware, you can enhance your Node.js applications' modularity, reusability, and maintainability.
Hello Guys,
Welcome to the Javascript Interview series. My aim is to prepare every one of you for any kind of interview related Javascript, it's libraries, frameworks and RTE(Run time environments).
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