Master programming syntax, solve interactive challenges & run live code in Syntaxis Explore Arena →
menu_book Course Curriculum (Express.js) expand_more
Application Basics
create express app listen server app settings environment config router mounting route parameters query parameters request body response send response json
Routing
GET routes POST routes PUT routes PATCH routes DELETE routes multiple handlers route patterns express Router nested routers router param
Middleware
application middleware router middleware built-in json middleware urlencoded middleware static middleware custom middleware error middleware middleware order request timing request ID logging middleware
Responses
status codes response headers redirect download sendFile content negotiation cookies clearCookie stream response ETag
Validation & Security
input validation sanitization CORS Helmet headers rate limiting authentication middleware authorization middleware secure cookies proxy trust body size limits
Persistence
database connection repository boundary async route handler transaction boundary N+1 avoidance cache layer pagination filtering sorting graceful DB shutdown
Testing & Errors
404 handler central error handler async errors validation errors route unit test integration test with Supertest mock dependency health endpoint readiness endpoint structured error response
Production
environment variables reverse proxy trust proxy process signals graceful shutdown compression static cache headers structured logs metrics hook deployment checklist
Express.js / Testing & Errors

404 handler

Learn 404 handler in Express.js with a dedicated explanation, a topic-specific example, edge guidance, and a mastery check.

12 min read • Advanced
expressjs-062.js
javascript 
app.use((req,res)=>res.status(404).json({error:"not_found",path:req.path}));
What to watch
Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

404 handler Mastery Check →
← PREVIOUS
graceful DB shutdown
NEXT →
central error handler