Understand-Anything/understand-anything-plugin/skills/understand/frameworks/express.md

Express Framework Addendum

Injected into file-analyzer and architecture-analyzer prompts when Express is detected. Do NOT use as a standalone prompt — always appended to the base prompt template.

Express Project Structure

When analyzing an Express project, apply these additional conventions on top of the base analysis rules.

Canonical File Roles

File / Pattern	Role	Tags
app.js, app.ts	Application entry point — creates Express app, mounts middleware and routes	entry-point, config
server.js, server.ts, index.js, index.ts	Server bootstrap — starts HTTP listener, may import app	entry-point, config
routes/*.js, routes/*.ts	Route definitions — map HTTP methods and paths to handlers	api-handler, routing
controllers/*.js, controllers/*.ts	Request handlers — process requests, orchestrate services, return responses	api-handler, service
models/*.js, models/*.ts	Data models — Mongoose schemas, Sequelize models, or plain data definitions	data-model
middleware/*.js, middleware/*.ts	Middleware functions — authentication, logging, validation, error handling	middleware
services/*.js, services/*.ts	Business logic — domain operations decoupled from HTTP layer	service
db/*.js, db/*.ts, database/*.js	Database connection and configuration	data-model, config
config/*.js, config/*.ts	Application configuration — environment variables, feature flags	config
validators/*.js, validators/*.ts	Request validation schemas (Joi, Zod, express-validator)	validation, utility
utils/*.js, utils/*.ts	Shared utility functions	utility
tests/*.js, test/*.js, __tests__/*.js	Unit and integration tests	test

Edge Patterns to Look For

Route mounting — When app.use('/api/users', usersRouter) mounts a router, create depends_on edges from the main app to the router module. These edges represent the HTTP routing tree.

Middleware chain — When app.use(cors()), app.use(authMiddleware), or router.use(validate) registers middleware, create middleware edges from the app or router to the middleware function. Order matters — middleware executes in registration order.

Controller-to-service calls — When a controller imports and calls a service function, create depends_on edges from the controller to the service. This represents the separation between HTTP handling and business logic.

Model relationships — When models reference each other (Mongoose ref, Sequelize associations), create depends_on edges between model files with descriptions indicating the relationship type.

Architectural Layers for Express

Assign nodes to these layers when detected:

Layer ID	Layer Name	What Goes Here
layer:api	API Layer	routes/, controllers/, request validators
layer:data	Data Layer	models/, db/, migration files, seeders
layer:service	Service Layer	services/, business logic modules
layer:middleware	Middleware Layer	middleware/, error handlers, authentication, logging
layer:config	Config Layer	app.js, config/, environment setup, server.js
layer:utility	Utility Layer	utils/, helpers/, shared pure functions
layer:test	Test Layer	tests/, __tests__/, *.test.js, *.spec.js

Notable Patterns to Capture in languageLesson

• Middleware chain (req, res, next): Express processes requests through a pipeline of middleware functions — each receives the request, response, and a next() callback to pass control forward
• Error-handling middleware (4 params): Middleware with signature (err, req, res, next) catches errors — must be registered after all routes to act as a global error handler
• Router modularity: express.Router() creates modular, mountable route handlers that can be composed into the main app at different path prefixes
• MVC pattern: Express apps commonly separate concerns into Models (data), Views (response formatting), and Controllers (request handling)
• Body parsing and validation: Request body parsing (express.json(), express.urlencoded()) and validation (Joi, Zod, express-validator) are middleware concerns applied before route handlers