Build a REST API with Node.js and Express (CRUD Example)

import express from "express";
import { z } from "zod";

const app = express();
app.use(express.json());

let nextId = 4;
const books = [
  { id: 1, title: "Godan", author: "Premchand", year: 1936, genre: "fiction" },
  { id: 2, title: "Wings of Fire", author: "A. P. J. Abdul Kalam", year: 1999, genre: "biography" },
  { id: 3, title: "The Guide", author: "R. K. Narayan", year: 1958, genre: "fiction" },
];

const BookSchema = z.object({
  title: z.string().trim().min(1).max(200),
  author: z.string().trim().min(1).max(100),
  year: z.number().int().min(1000).max(2100),
  genre: z.enum(["fiction", "biography", "science", "history"]),
});

function parseOr400(schema, data, res) {
  const result = schema.safeParse(data);
  if (!result.success) {
    res.status(400).json({
      error: "Validation failed",
      details: result.error.issues.map((i) => `${i.path.join(".")}: ${i.message}`),
    });
    return null;
  }
  return result.data;
}

function findBook(req, res) {
  const book = books.find((b) => b.id === Number(req.params.id));
  if (!book) res.status(404).json({ error: "Book not found" });
  return book;
}

// List with filter, sort and pagination
app.get("/api/books", (req, res) => {
  const { genre, author, sort = "id", page = "1", limit = "10" } = req.query;
  let result = books;
  if (genre) result = result.filter((b) => b.genre === genre);
  if (author) result = result.filter((b) => b.author.toLowerCase().includes(author.toLowerCase()));

  const desc = sort.startsWith("-");
  const field = desc ? sort.slice(1) : sort;
  if (!["id", "title", "year"].includes(field)) return res.status(400).json({ error: "Cannot sort by " + field });
  result = result.toSorted((a, b) => (a[field] > b[field] ? 1 : a[field] < b[field] ? -1 : 0) * (desc ? -1 : 1));

  const pageNum = Math.max(1, Number(page) || 1);
  const size = Math.min(50, Math.max(1, Number(limit) || 10));
  const start = (pageNum - 1) * size;
  res.json({ data: result.slice(start, start + size), page: pageNum, limit: size, total: result.length });
});

app.get("/api/books/:id", (req, res) => {
  const book = findBook(req, res);
  if (book) res.json({ data: book });
});

app.post("/api/books", (req, res) => {
  const data = parseOr400(BookSchema, req.body, res);
  if (!data) return;
  const book = { id: nextId++, ...data };
  books.push(book);
  res.status(201).location(`/api/books/${book.id}`).json({ data: book });
});

app.put("/api/books/:id", (req, res) => {
  const book = findBook(req, res);
  if (!book) return;
  const data = parseOr400(BookSchema, req.body, res);        // PUT needs every field
  if (!data) return;
  Object.assign(book, data);
  res.json({ data: book });
});

app.patch("/api/books/:id", (req, res) => {
  const book = findBook(req, res);
  if (!book) return;
  const data = parseOr400(BookSchema.partial(), req.body, res);   // PATCH: any subset of fields
  if (!data) return;
  Object.assign(book, data);
  res.json({ data: book });
});

app.delete("/api/books/:id", (req, res) => {
  const book = findBook(req, res);
  if (!book) return;
  books.splice(books.indexOf(book), 1);
  res.sendStatus(204);
});

app.listen(3000);

curl -s "localhost:3000/api/books?genre=fiction&sort=-year"
curl -s "localhost:3000/api/books?limit=2&page=2"
curl -s localhost:3000/api/books/2

curl -s -w " [%{http_code}]\n" -X POST localhost:3000/api/books -H "Content-Type: application/json" -d '{"title":"A Brief History of Time","author":"Stephen Hawking","year":1998,"genre":"science"}'
curl -s -w " [%{http_code}]\n" -X POST localhost:3000/api/books -H "Content-Type: application/json" -d '{"title":"","year":"1988","genre":"poetry"}'
curl -s -w " [%{http_code}]\n" -X PATCH localhost:3000/api/books/4 -H "Content-Type: application/json" -d '{"year":1988}'
curl -s -w " [%{http_code}]\n" -X PUT localhost:3000/api/books/4 -H "Content-Type: application/json" -d '{"year":1988}'
curl -s -w " [%{http_code}]\n" -X DELETE localhost:3000/api/books/4
curl -s -w " [%{http_code}]\n" localhost:3000/api/books/4