Step-by-step articles on Backend, part of our Web Development collection.
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If you learned Node.js a few years ago, you probably install packages for things the runtime now does itself. Here's a tour of built-ins in current LTS versions. fetch, WebSocket and Web APIs const res = await fetch('https://api.github.com/repos/nodejs/node');...
FastAPI is a Python web framework built on type hints. You describe your inputs and outputs with types, and FastAPI validates requests, serialises responses and generates interactive API docs for you. Install and run pip install "fastapi[standard]" fastapi dev...
A well-designed REST API is predictable: once a developer has used one endpoint, they can guess how the others work. These conventions get you most of the way there. URLs name resources, not actions GET /orders list orders POST /orders create an order GET /ord...
Node.js ships a full test runner. For many backends and libraries it replaces Jest or Mocha entirely, with zero dependencies. Writing tests // test/cart.test.js import { describe, it, beforeEach } from 'node:test'; import assert from 'node:assert/strict'; impo...
Pydantic models are the heart of FastAPI. Every field type and constraint becomes runtime validation and documentation. Field constraints from typing import Annotated from pydantic import BaseModel, EmailStr, Field class SignupRequest(BaseModel): email: EmailS...
Any list endpoint needs pagination. The two main approaches behave very differently on large or fast-changing data. Offset pagination GET /articles?page=3&per_page=20 SELECT * FROM articles ORDER BY published_at DESC LIMIT 20 OFFSET 40; Pros: simple, lets user...
Node.js supports two module systems: the original CommonJS ( require ) and standard ES modules ( import ). New projects should use ESM, but you'll meet both. Turning on ESM // package.json { "type": "module" } With "type": "module" , .js files are ESM. Without...
FastAPI's Depends lets endpoints declare what they need (a database session, the current user, pagination settings) and FastAPI provides it. Dependencies can depend on other dependencies, and they're easy to replace in tests. A simple dependency from typing im...
Once other people depend on your API, every change can break someone. Versioning gives you room to evolve without surprises. First: avoid breaking changes Usually safe (additive): Adding a new endpoint. Adding an optional request field. Adding a field to a res...
Configuration such as database URLs and API keys belongs in environment variables, not in code. Node.js can now load .env files itself. Loading from the command line # .env DATABASE_URL=postgres://localhost:5432/app PORT=3000 node --env-file=.env src/server.js...
SQLAlchemy 2.0 brought a cleaner, fully typed API and first-class async support. Combined with the asyncpg driver it's a solid choice for FastAPI apps. Install pip install "sqlalchemy[asyncio]" asyncpg alembic Engine and session # db.py from sqlalchemy.ext.asy...
A client sends POST /payments , the network times out, and it retries. Did the first request succeed? Without protection, the customer may be charged twice. Idempotency keys make retries safe. The contract POST /payments Idempotency-Key: 7f3b2c1e-9a4d-4e8b-a1f...
Reading a 5 GB log file with fs.readFile loads all 5 GB into memory. Streams process data in small chunks, so memory use stays flat no matter how big the input is. The four stream types Readable - a source (file, HTTP request, database cursor). Writable - a de...
This guide adds a /auth/token login endpoint that returns a JWT, and a dependency that protects routes. It follows the pattern FastAPI's own docs use. Install pip install pyjwt "pwdlib[argon2]" Hashing and tokens # security.py from datetime import datetime, ti...
Every API needs an error format, and many invent their own. Problem Details (RFC 9457, which replaced RFC 7807) is a standard JSON shape for HTTP API errors that clients and tools already understand. The format HTTP/1.1 403 Forbidden Content-Type: application/...
Node.js runs your JavaScript on a single thread. That's fine for I/O, but a CPU-heavy task (resizing images, parsing a huge file, heavy maths) blocks the event loop, and every other request waits. Spot the problem app.get('/report', (req, res) => { const resul...
FastAPI apps are easy to test because endpoints are plain functions behind an ASGI app, and dependencies can be swapped per test. A first test # test_books.py from fastapi.testclient import TestClient from main import app client = TestClient(app) def test_crea...
GraphQL and REST both work well. The right choice depends on your clients, your data and your team, not on which one is newer. The core difference With REST, the server decides the shape of each endpoint's response. With GraphQL, the client asks for exactly th...
Express 5 finally handles async route handlers properly: if an async handler throws or returns a rejected promise, the error goes to your error middleware. No more express-async-errors or wrapping every route in try/catch. Async handlers just work app.get('/us...
Two common needs in API servers: running code once when the app starts or stops, and doing a bit of work after the response is sent. Lifespan: startup and shutdown from contextlib import asynccontextmanager import httpx from fastapi import FastAPI @asynccontex...
A GraphQL server needs two things: a schema describing types and operations, and resolvers that fetch the data for each field. Setup npm install @apollo/server graphql Schema and resolvers // server.js import { ApolloServer } from '@apollo/server'; import { st...
Most API breaches come from a few well-known mistakes. Work through this checklist for every Node.js service you deploy. 1. Validate every input import { z } from 'zod'; const CreateOrder = z.object({ productId: z.uuid(), quantity: z.number().int().min(1).max(...
Some responses shouldn't wait until everything is ready: large exports, progress updates, or text from an LLM. FastAPI's StreamingResponse sends data as your generator produces it. Streaming a large CSV from fastapi.responses import StreamingResponse @app.get(...
Fetch 50 books with their authors, and a naive server runs 1 query for the books plus 50 queries for authors. That's the N+1 problem , and it's the most common GraphQL performance issue. Why it happens Book: { // called once per book, each with its own query a...
Containers and process managers stop your app by sending SIGTERM . If you exit immediately, requests in progress fail and database transactions are cut off. A graceful shutdown finishes the current work first. The steps Stop accepting new connections. Let in-f...
A production FastAPI deployment is usually a container running an ASGI server behind a reverse proxy or load balancer. Dockerfile FROM python:3.13-slim # uv for fast, reproducible installs COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv WORKDIR /...
OpenAPI (formerly Swagger) is a standard, machine-readable description of a REST API. One spec file can produce interactive docs, client SDKs, mock servers and request validation. A minimal spec openapi: 3.1.0 info: title: Orders API version: 1.0.0 servers: -...
A memory leak shows up as memory that keeps climbing until the process is killed or restarts. The fix starts with proving where the memory goes. 1. Confirm the leak setInterval(() => { const { heapUsed, rss } = process.memoryUsage(); console.log(`heap ${(heapU...
A single main.py is perfect for a prototype. As the API grows, split it by feature so each area of the product lives together. A feature-based layout app/ main.py # creates the app, includes routers config.py # settings from environment db.py # engine, session...
Rate limits protect your API from abuse, runaway scripts and accidental traffic spikes, and keep things fair between customers. Common algorithms Fixed window - count requests per calendar minute. Simple, but allows bursts at window edges (100 at 12:00:59 and...
