Router handlers, Request/Response typing
Type Express route handlers: params, query, and JSON bodies; send typed responses with res.json and reusable DTOs.
Router handlers, Request/Response typing is a free TypeScript Academy lesson on CoddyKit. This is lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, and your progress syncs across the web and the CoddyKit app. The TypeScript Academy course includes 3 lessons in total.
Intro
Goal: Wire a small Express API with strict types. You will type route params, query, and JSON bodies, then return typed JSON with res.json.
- DTO interfaces
Request<P, Res, Body, Q>- Typed
res.json
Server setup
Initialize Express and enable JSON parsing. Keep the health endpoint small and typed with Request/Response.
import express, { Request, Response } from "express"
const app = express()
app.use(express.json())
app.get("/", (_req: Request, res: Response) => {
res.type("text/plain").send("OK")
})
app.listen(3000, () => console.log("http://localhost:3000"))Params & query
Type each slot explicitly: Params, Query, and ResBody. Autocomplete helps avoid typos.
import { Request, Response } from "express"
type Params = { id: string }
type Query = { verbose?: "1" | "0" }
type ResBody = { id: string; name: string; details?: string }
export function getUser(req: Request<Params, ResBody, unknown, Query>, res: Response<ResBody>) {
const { id } = req.params
const { verbose } = req.query
const body: ResBody = { id, name: "Ada", details: verbose === "1" ? "Loves math" : undefined }
return res.status(200).json(body)
}Typed body & res
Annotate the body for POST/PUT, plus a typed response. Your DTOs double as documentation.
import { Request, Response } from "express"
type CreateUserBody = { name: string }
type CreateUserRes = { id: string; name: string }
export function createUser(req: Request<{}, CreateUserRes, CreateUserBody>, res: Response<CreateUserRes>) {
const { name } = req.body
const result: CreateUserRes = { id: "u_1", name }
return res.status(201).json(result)
}Wire routes
Compose small, typed handlers. Route params are validated by matching the template (e.g., :id).
import express from "express"
import { getUser } from "./getUser"
import { createUser } from "./createUser"
const app = express()
app.use(express.json())
app.get("/users/:id", getUser)
app.post("/users", createUser)
app.listen(3000, () => console.log("http://localhost:3000"))Tips
Tips:
- Keep DTOs small and reuse across handlers.
- Prefer union literals for constrained query values.
- Return precise status codes and typed JSON.
Express typing check
Quick check: How do you type an Express handler with params and JSON body?
Recap
Recap: You typed route params, query, bodies, and responses. The same pattern scales to routers and middlewares.
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Frequently Asked Questions
Is the “Router handlers, Request/Response typing” lesson free?
Yes — the full text of “Router handlers, Request/Response typing” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO. The TypeScript Academy course includes 3 lessons in total.
What will I learn in “Router handlers, Request/Response typing”?
Type Express route handlers: params, query, and JSON bodies; send typed responses with res.json and reusable DTOs. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start TypeScript Academy?
No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 3.
How long does the “Router handlers, Request/Response typing” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this TypeScript Academy lesson?
Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Router handlers, Request/Response typing
- Schema validation with zod & inference to TS
- Error middleware & result types