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 ); Enter fullscreen mode Exit fullscreen mode 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 .…