#node.js

Express 4 to 5 Migration Planner for Node.js APIs: path-to-regexp 8 Route Syntax for Named Wildcards and Optional Braces, Removed Methods, req.query Getter and Simple Parser, Async Error Handling, Middleware Compatibility, and a Test Plan

Upgrade an Express 4 app to Express 5 route by route: rewrite wildcard, optional, and regex routes for the new path syntax, replace removed methods like app.del, req.param, and res.json with a status argument, handle the read only req.query and the simple query parser, drop try and catch wrappers that async error handling makes redundant, check middleware, and test before release.

Act as a Node.js backend engineer who has upgraded production Express 4 APIs to Express 5, reviews route files for a living, and has shipped the bug where a wildcard route silently stopped matching after the path syntax changed. Inputs: - Current Express version, Node.js version, and package.json dependencies that touch Express: [Stack] - Route definitions and router files (paste the app.get, router.use, and similar lines): [Routes] - Code that uses request and response helpers, especially req.param, req.query writes, res.json with two arguments, res.send with a number, res.redirect, and res.sendfile: [HandlerCode] - Middleware list in order, including third party packages and any that modify req.query: [Middleware] - Test setup and how the API is deployed: [Tests] - Output format: [Format] Generate: 1. A readiness check: Express 5 needs Node.js 18 or newer, so confirm Stack first; list each dependency in Stack and Middleware with a note on whether its docs state Express 5 support or need checking. 2. A route syntax table for every line in Routes using path-to-regexp 8 rules: wildcards must be named (/files/*splat, and /{*splat} to also match the root), optional parts use braces (/users{/:id}) instead of a trailing question mark, inline regex such as /:id(\d+) is removed and becomes validation in the handler or a router.param check, and reserved characters must be escaped. Note that wildcard params arrive as arrays of segments. 3. A removed and changed API list from HandlerCode, each with before and after code: app.del to app.delete, req.param(name) to req.params, req.body, or req.query, res.json(obj, status) to res.status(status).json(obj), res.send(number) to res.sendStatus, res.sendfile to res.sendFile, res.redirect('back') to the Referrer header with a fallback, and the pluralized req.acceptsCharsets, acceptsEncodings, and acceptsLanguages. 4. Query and body changes: req.query is a getter and cannot be reassigned, the default query parser is now simple, how to opt back in with app.set('query parser', 'extended') if nested objects are used, express.urlencoded defaults to extended false, and req.body is undefined when no body parser ran. 5. Async error handling: rejected promises and thrown errors in async handlers now reach next(err), so list which try and catch wrappers or express-async-errors style packages can be removed, and confirm the error handler still has four arguments. 6. Other behavior changes to check: res.status accepts only integers from 100 to 999, express.static ignores dotfiles by default, and any code that depended on old behavior. 7. A migration order: run the official codemods if available (check the Express migration guide), fix routes, fix handlers, update middleware, then tests. 8. A test plan: one request per changed route including root, nested, optional, and invalid id cases, query parsing tests for nested parameters, and an error path test for an async handler. Constraints: - Only rewrite code shown in the Inputs. Never invent routes, packages, or versions. - Flag anything you cannot confirm as "check the Express 5 migration guide". No em dashes.