Middleware ordering and chaining

When using Express, treat middleware registration as an HTTP request-processing pipeline: middleware executes in the order you add it, and the chain advances only if your middleware calls `next()`.

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Prompt

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When using Express, treat middleware registration as an HTTP request-processing pipeline: middleware executes in the order you add it, and the chain advances only if your middleware calls next().

Apply this standard:

  • Use the canonical middleware signature in code/docs: (req, res, next).
  • Register middleware with app.use(...) (and any static middleware) in the exact order you need.
  • Call next() whenever the request should continue to later middleware/route handlers; if you don’t call it, the request-response cycle stops.
  • Stack built-in and third-party middleware intentionally; later middleware can depend on earlier changes to req/res.

Example:

const express = require('express')
const cors = require('cors')
const morgan = require('morgan')
const app = express()

// 1) Parse/prepare request (built-in)
app.use(express.json())

// 2) Middleware behavior depends on order (third-party)
app.use(cors())
app.use(morgan('tiny'))

// 3) Intercept/transform request, then continue
app.use((req, res, next) => {
  req.requestId = req.header('x-request-id')
  next() // must be called to reach the next middleware/route
})

// 4) Serve static assets via middleware (register intentionally)
app.use(express.static('public'))

app.get('/', (req, res) => res.send('Hello'))

app.listen(3000)

Outcome: predictable HTTP behavior, fewer “why didn’t my route run?” issues, and middleware effects (auth, logging, parsing, static serving) that are consistent across the app.

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