Intermediate code explainers

go

package middleware
 
import (
	"net/http"

Building a CORS middleware in Gin

cors middleware closures

Intermediate 9 steps

javascript

const express = require('express');
const router = express.Router();
const db = require('../db');

Building a paginated articles endpoint in Express

pagination input-validation async-await

Intermediate 8 steps

python

from collections import OrderedDict
from typing import Any, Hashable, Optional

Building an LRU cache with OrderedDict

caching eviction data-structures

Intermediate 6 steps

typescript

import { Injectable, NotFoundException } from '@nestjs/common';
import { EventEmitter2, OnEvent } from '@nestjs/event-emitter';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';

Decoupling side effects with NestJS events

event-driven decoupling dependency-injection

Intermediate 7 steps

java

public final class ZipExtractor {
 
    private final Path targetDir;

Extracting a zip safely in Java

path-traversal streams file-io

Intermediate 8 steps

ruby

class SignupValidator
  EMAIL_REGEX = /\A[^@\s]+@[^@\s]+\.[^@\s]+\z/
  MIN_PASSWORD_LENGTH = 8

Building a plain-Ruby signup validator

validation regex default-hash

Intermediate 7 steps

php

<?php
 
namespace App\Jobs;

Building a unique queued job in Laravel

queues background-jobs idempotency

Intermediate 7 steps

rust

use std::fs;
use std::path::Path;
 
use regex::Regex;

Redacting emails in a file with Rust

regex file-io closures

Intermediate 6 steps

javascript

import { useState, useCallback, memo } from 'react';
 
const TodoItem = memo(function TodoItem({ todo, onToggle, onRemove }) {
  return (

Preventing re-renders in a React todo list

memoization usecallback referential-stability

Intermediate 8 steps

python

from flask import Flask, g, jsonify, request, abort
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker

Per-request SQLAlchemy sessions in Flask

database sessions request lifecycle connection management

Intermediate 7 steps

typescript

import { Component, OnInit, inject } from '@angular/core';
import { ActivatedRoute, Router } from '@angular/router';
import { FormBuilder } from '@angular/forms';
import { debounceTime, map } from 'rxjs/operators';

Syncing an Angular filter form with the URL

reactive-forms query-params rxjs

Intermediate 8 steps

ruby

class QueryBuilder
  def initialize(table)
    @table = table
    @wheres = []

How a chainable SQL query builder works

fluent-interface method-chaining builder-pattern

Intermediate 8 steps

php

<?php
 
declare(strict_types=1);

An immutable typed collection in PHP

immutability value-objects iterators

Intermediate 8 steps

go

package main
 
import (
	"context"

Graceful shutdown for a Gin server in Go

graceful-shutdown signals goroutines

Intermediate 6 steps

rust

use std::fs::{File, OpenOptions};
use std::io::{self, Write};
use std::path::Path;

A buffered log writer in Rust

buffering raii file-io

Intermediate 9 steps

javascript

import { useState, useEffect, useRef, useCallback } from "react";
 
function useDebouncedValue(value, delay) {
  const [debounced, setDebounced] = useState(value);

Debounced autosave in React

debouncing custom-hooks abort-controller

Intermediate 8 steps

javascript

import { lazy, Suspense } from "react";
import { Routes, Route, NavLink } from "react-router-dom";
import ErrorBoundary from "./components/ErrorBoundary";
import Spinner from "./components/Spinner";

Lazy-loaded routes in React

code-splitting lazy-loading routing

Intermediate 6 steps

python

from fastapi import APIRouter, Depends, Response, status
from sqlalchemy.orm import Session
 
from .database import get_db

Building a REST article resource in FastAPI

dependency injection rest api orm

Intermediate 8 steps