How does Middleware work in Express?

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This article is an adapted excerpt from the Express API Validation Essentials book . It will teach you a complete API validation strategy that you can start using in your Express applications today.

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app.get("/user", function routeHandlerMiddleware(request, response, next) {
    // execute something
});
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.1)

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middleware:

/**
 * @param {Object} request - Express request object (commonly named `req`)
 * @param {Object} response - Express response object (commonly named `res`)
 * @param {Function} next - Express `next()` function
 */
function middlewareFunction(request, response, next) {
    // execute something
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.2)

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function plainMiddlewareFunction(request, response, next) {
    console.log(`The request method is ${request.method}`);

    /**
     * Ensure the next middleware function is called.
     */
    next();
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.3)

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middleware :

function errorHandlingMiddlewareFunction(error, request, response, next) {
    console.log(error.message);

    /**
     * Ensure the next error handling middleware is called.
     */
    next(error);
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.4)

, next()



, .

function anotherMiddlewareFunction(request, response, next) {
    const error = new Error("Something is wrong");

    /**
     * This will cause Express to start executing error
     * handling middleware.
     */
    next(error);
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.5)

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app.get("/", someMiddleware, routeHandlerMiddleware, errorHandlerMiddleware);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.6)

Express Router. middleware . , middleware , , .

import express from "express";

const router = express.Router();

router.use(someMiddleware);

router.post("/user", createUserRouteHandler);
router.get("/user/:user_id", getUserRouteHandler);
router.put("/user/:user_id", updateUserRouteHandler);
router.delete("/user/:user_id", deleteUserRouteHandler);

router.use(errorHandlerMiddleware);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.7)

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app.use(someMiddleware);

// define routes

app.use(errorHandlerMiddleware);
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

( 1.8)

, app.use(someMiddleware)



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"Express API Validation Essentials". API, Express- .

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"Node.js Developer". , , Demo Day , 28 .

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