5 Express.js Middleware Patterns You'll Use in Every App

Middleware is what makes Express powerful. These patterns show up in every production app.

What Is Middleware?

// A function that has access to req, res, and next function myMiddleware ( req , res , next ) { // Do something with the request console . log ( ` ${ req . method } ${ req . path } ` );

// Either respond (end the chain) if ( req . path === ' /health ' ) { return res . json ({ status : ' ok ' }); }

// Or pass control to the next middleware next (); }

app . use ( myMiddleware );

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Pattern 1: Request Logging & Correlation IDs

import { randomUUID } from ' crypto ' ;

// Add a unique ID to every request for tracing function requestId ( req , _res , next ) { req . id = req . headers [ ' x-request-id ' ] || randomUUID (); next (); }

// Structured logging with context function logger ( req , _res , next ) { const start = Date . now ();

_res . on ( ' finish ' , () => { const duration = Date .…