Stop 05 · Express.js & Web FrameworksProjects · 1/3

REST API for Todo App

In short

The todo API is the 'hello world' of backends for a reason: it uses every CRUD operation. Build it properly once and you'll reuse the pattern in every project.

A full CRUD API for managing todos — the classic first Express project, exercising routing, validation, and connecting to a real database.

The mascot sticks colourful notes on a corkboard and ticks one with a marker.

Think of it like this

The sticky-note board

On your hostel wall, you stick notes, read them, tick some off, and peel others away. Create, read, update, delete. Your todo API does exactly this, except the board is a database and the notes are JSON.

Watch it happen

CRUD in five requests

Client

Todo API

Store

POST /todos

1/6Body { "title": "Submit DBMS assignment" }. The API validates it.

The big ideas

What you need to know

Five endpoints

GET /todos, GET /todos/:id, POST /todos, PATCH /todos/:id, DELETE /todos/:id.

Correct status codes

201 on create, 204 on delete, 404 for a missing id, 400 for a bad body.

Validate every write

Title required and trimmed, sensible max length, done must be a boolean.

Filter the list

Support GET /todos?done=false so the app can show only pending tasks.

See it in code

Walk through the code

1const todos = new Map();2let nextId = 1;3app.patch("/todos/:id", (req, res) => {4  const todo = todos.get(Number(req.params.id));5  if (!todo) return res.status(404).json({ error: "Todo not found" });6  const { title, done } = req.body;7  if (title !== undefined && (typeof title !== "string" || !title.trim())) {8    return res.status(400).json({ error: "title must be a non-empty string" });9  }10  if (done !== undefined && typeof done !== "boolean") {11    return res.status(400).json({ error: "done must be true or false" });12  }13  if (title !== undefined) todo.title = title.trim();14  if (done !== undefined) todo.done = done;15  res.json(todo);16});