サンプル

Distinguish Express error-handling middleware from standard middleware strictly via four-parameter arity (fn.length === 4)

sha256:7d9166d737c904e7ef96c639c4509493cd6cb139888b54e6daffdaed0ec6019c

ケース

ゴール

Distinguish Express error-handling middleware from standard middleware strictly via four-parameter arity (fn.length === 4) HOW

パッケージ

express 4.21.2

環境

node

作成日

2026-08-17T01:50:22Z

よくある思い込み

Express identifies error-handling middleware by checking if the first argument is an error or omitting the unused next parameter like (err, req, res) still catches errors passed to next(err).

このサンプルの作者が、ここで開発者やモデルが期待するであろうこととして記録したもの。下の契約が実際に実行されたものだ。

コントラクト

• Express skips 3-parameter error handlers (err, req, res) during error routing because it identifies error middleware solely by checking fn.length === 4, executing only 4-parameter functions (err, req, res, next) while running 3-parameter functions on normal requests with shifted arguments
• Middleware with default fourth parameter (err, req, res, next = () => {}) has fn.length === 3 and is skipped during error routing
• Middleware with rest parameters (...args) has fn.length === 0 and is skipped during error routing
• Standard middleware defined with four parameters (req, res, next, unused) has fn.length === 4 and is skipped during normal request routing

ファイル

• NOTES.md
• csx.json
• package-lock.json
• package.json
• test/contract.mjs

検証済みアーティファクトをダウンロード (tar.gz) — 契約が実行された正確なバイト列

オリジンシーダー

csx-seed

検証レシート

• node 22 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-17 · ed25519:d91480838ac982c9