Code Explainers

Browse the library

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
go 
package middleware
 
import (
	"context"

How a request-timeout middleware works in Gin

middleware context goroutines
Advanced 6 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
java 
@Entity
@Table(name = "invoices")
@FilterDef(name = "tenantFilter", parameters = @ParamDef(name = "tenantId", type = String.class))
@Filter(name = "tenantFilter", condition = "tenant_id = :tenantId")

Multi-tenant row filtering with Hibernate in Spring

multi-tenancy hibernate filters request interceptor
Advanced 7 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
java 
@Configuration
@EnableIntegration
public class OrderProcessingFlow {
 

Building an order pipeline with Spring Integration

messaging pipeline enterprise integration patterns
Intermediate 9 steps
go 
package token
 
import (
	"crypto/rand"

Generating secure random tokens in Go

cryptography randomness encoding
Intermediate 5 steps
rust 
use axum::{
    extract::{FromRef, FromRequestParts},
    http::{request::Parts, StatusCode},
    response::{IntoResponse, Response},

A custom API-key extractor in Axum

authentication extractors trait-implementation
Advanced 8 steps