Due Dates

Part of the REST APIs section of Coddy's Node.js journey. Lesson 25 of 25.

Tasks get a due date, and the board shows which ones are late. A date without a time travels as an ISO string, 2026-03-15, which zod checks with z.iso.date():

z.iso.date().safeParse('2026-07-01').success   // true
z.iso.date().safeParse('2026-02-30').success   // false: no such day
'2026-03-01' < '2026-03-15'                    // true

ISO dates have the same length and put the year first, so comparing them as strings gives time order. A fixed path like /overdue must come before /:id in the router: Express tries routes in order, and /:id matches any word.

Challenge

Easy

The board shows which tasks are late. Give tasks an optional due date, and add a list of the overdue ones.

In routes/tasks.js, add an optional due field to the Task schema, checked with z.iso.date(). It accepts only real dates written YYYY-MM-DD. "2026-03-15" passes, while "15/03/2026", "2026-02-30" and "tomorrow" get the usual 400 invalid_body error. Make sure POST saves due on the new task.
Add GET /api/v1/tasks/overdue to the router. Declare it above the /:id route, or Express sends overdue to /:id as an id.
The route reads the date to compare with from ?today=, for example ?today=2026-03-20. Without today, it uses the current date written YYYY-MM-DD. A today that is not a real date, like ?today=soon, gets status 400:
```
{ "error": { "code": "invalid_query", "message": "today must be a date like 2026-03-10" } }
```
The route returns a plain array of tasks, not the page object the list returns. A task is overdue when all three hold: it is not done, it has a due date, and that date is before today. A task due on today itself is not overdue yet. Sort the array by due, earliest date first.

Try it: on a fresh Run, POST { "title": "Renew the lease", "due": "2026-03-15" } and then { "title": "File the taxes", "due": "2026-03-01" } to /api/v1/tasks. Both return 201 with their due. Then GET /api/v1/tasks/overdue?today=2026-03-20 returns the earlier due date first (your createdAt times will differ):

[
  { "id": 5, "title": "File the taxes", "done": false, "labels": [], "due": "2026-03-01", "createdAt": "2026-10-30T09:15:02.118Z" },
  { "id": 4, "title": "Renew the lease", "done": false, "labels": [], "due": "2026-03-15", "createdAt": "2026-10-30T09:14:40.006Z" }
]

GET /api/v1/tasks/overdue?today=2026-03-15 returns only "File the taxes". GET /api/v1/tasks/overdue?today=soon returns 400 with code invalid_query.

Try it yourself

import { Router } from 'express';
import { z } from 'zod';
import { config } from '../config.js';
import { sendError, sendInvalid } from '../errors.js';
import { nextId, tasks } from '../store.js';

const router = Router();

// A whole task, as PUT sends it. .strict() refuses fields it does not list.
const Task = z
    .object({
        title: z.string().trim().min(1).max(100),
        done: z.boolean(),
        labels: z.array(z.string().trim().min(1).max(20)).max(5).optional(),
    })
    .strict();
const NewTask = Task.partial({ done: true });
const TaskChanges = Task.partial();
const SORT_FIELDS = ['title', 'createdAt'];

// True when another task already has this title, in any case.
const titleTaken = (title, exceptId) =>
    tasks.some((t) => t.id !== exceptId && t.title.toLowerCase() === title.toLowerCase());

router.get('/', (req, res) => {
    const { done, q, sort, label } = req.query;
    let list = tasks;
    if (done !== undefined) {
        if (done !== 'true' && done !== 'false') {
            return sendError(res, 400, 'invalid_query', 'done must be true or false');
        }
        list = list.filter((t) => t.done === (done === 'true'));
    }
    if (q !== undefined) {
        const words = String(q).toLowerCase();
        list = list.filter((t) => t.title.toLowerCase().includes(words));
    }
    if (label !== undefined) {
        list = list.filter((t) => t.labels.includes(String(label)));
    }
    if (sort !== undefined) {
        const field = String(sort).startsWith('-') ? String(sort).slice(1) : String(sort);
        if (!SORT_FIELDS.includes(field)) {
            return sendError(
                res,
                400,
                'invalid_query',
                'sort must be title or createdAt, with - in front to reverse',
            );
        }
        const direction = String(sort).startsWith('-') ? -1 : 1;
        list = list.toSorted((a, b) => a[field].localeCompare(b[field]) * direction);
    }
    const page = req.query.page === undefined ? 1 : Number(req.query.page);
    const limit = req.query.limit === undefined ? config.pageSize : Number(req.query.limit);
    if (!Number.isInteger(page) || page < 1) {
        return sendError(res, 400, 'invalid_query', 'page must be a whole number from 1');
    }
    if (!Number.isInteger(limit) || limit < 1 || limit > 50) {
        return sendError(res, 400, 'invalid_query', 'limit must be a whole number from 1 to 50');
    }
    const start = (page - 1) * limit;
    res.json({
        items: list.slice(start, start + limit),
        page,
        total: list.length,
        pages: Math.ceil(list.length / limit),
    });
});

router.get('/:id', (req, res) => {
    const task = tasks.find((t) => t.id === Number(req.params.id));
    if (!task) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    res.json(task);
});

router.post('/', (req, res) => {
    const result = NewTask.safeParse(req.body);
    if (!result.success) {
        return sendInvalid(res, result.error);
    }
    const { title, done = false, labels = [] } = result.data;
    if (titleTaken(title)) {
        return sendError(res, 409, 'conflict', 'A task with this title already exists');
    }
    const task = { id: nextId(), title, done, labels, createdAt: new Date().toISOString() };
    tasks.push(task);
    res.status(201).location(`/api/v1/tasks/${task.id}`).json(task);
});

router.patch('/:id', (req, res) => {
    const task = tasks.find((t) => t.id === Number(req.params.id));
    if (!task) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    const result = TaskChanges.safeParse(req.body);
    if (!result.success) {
        return sendInvalid(res, result.error);
    }
    if (result.data.title !== undefined && titleTaken(result.data.title, task.id)) {
        return sendError(res, 409, 'conflict', 'A task with this title already exists');
    }
    Object.assign(task, result.data);
    res.json(task);
});

router.put('/:id', (req, res) => {
    const index = tasks.findIndex((t) => t.id === Number(req.params.id));
    if (index === -1) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    const result = Task.safeParse(req.body);
    if (!result.success) {
        return sendInvalid(res, result.error);
    }
    const { id, createdAt } = tasks[index];
    if (titleTaken(result.data.title, id)) {
        return sendError(res, 409, 'conflict', 'A task with this title already exists');
    }
    tasks[index] = { id, ...result.data, labels: result.data.labels ?? [], createdAt };
    res.json(tasks[index]);
});

router.delete('/:id', (req, res) => {
    const index = tasks.findIndex((t) => t.id === Number(req.params.id));
    if (index === -1) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    tasks.splice(index, 1);
    res.status(204).end();
});

export default router;