Implementación de Middlewares en Node.js sin Express

Learning how the Middleware pattern works in Node.js allows you to sequentially execute operations during a request. Although Express is known for using this pattern extensively, it is possible to implement it from scratch in Node.js. It is basically functions that manipulaterequests andresponses and can modify, add or remove properties depending on their function.

What is the Middleware pattern?

Middleware is a simple but powerful technique that allows you to handle Web requests by splitting the processing into independent stages. It is central to frameworks such as Express and consists of functions that are executed one after the other in a chain.

A middleware receives three main arguments:

• Request (req): the object containing information about the request made.
• Response (res): The object used to generate the response to the request.
• Next: A function that allows passing to the next Middleware in the chain.

Each Middleware can alter or enrich the objects received before passing them to the next one.

How to implement Middleware without Express?

Implementing your own Middlewares without Express is an effective way to understand its inner workings. Here is a quick description of how to perform a basic implementation using only Node.js.

Step by step implementation:

1. Create main function.

Declare a function called runMiddlewares that accepts request, response and an array of Middlewares.

1. Define individual Middlewares

Each Middleware is a separate, clearly identifiable function:

const middleware1  = (req, res, next)  =>  {    console.log('Middleware1 - Authentication');    next(); }; const  middleware2 = (req,  res,  next) => {     console.log('Middleware2 - Request processing');    next(); }; const middleware3 = (req, res,  next) => {    console.log('Middleware 3 - Completion');     next(); }; const middleware3 = (req,res, next) => { console.log('Middleware 3 - Completion'); next();};

1. Running Middlewares sequentially

Each Middleware is executed in sequential order using a recursive function:

        const runMiddlewares  = (req, res, middlewares)  =>  {    let index  =  0;    const next  =  ()  =>  {        if (index < middlewares.length)  {            const middleware  = middlewares[index++];            middleware(req, res, next);         }  xml-ph-0030@de

1. Launch execution

Finally, you must start this process by specifying the required parameters:

const req  =  {};const res  =  {};runMiddlewares(req, res, [middleware1, middleware2, middleware3]);

Why is the order of middleware important?

Middlewares are executed strictly in the order in which they are defined in their array. This allows for easy control of specific functionalities, such as authentication, validation, main processing and termination. This ensures that the logical order required for each task is followed.

Practical example of conditional middleware

As a further exercise, you can extend this implementation with conditional logic. For example, allow Middleware 3 to control the execution of Middleware 4:

• Middleware 3 checks for specific conditions.
• It decides whether or not to execute Middleware 4 using a conditional structure.

This exercise brings an additional layer of real-world utility to your middleware knowledge.

Try building your own version and share it!