Code Explainers

Browse the library

javascript 
import { useState, useEffect, useMemo } from 'react';
 
function useDebounce(value, delay = 300) {
  const [debounced, setDebounced] = useState(value);

Debounced search with cancellation in React

custom-hooks debounce abortcontroller
Intermediate 9 steps
java 
package com.example.payments.config;
 
import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotBlank;

Type-safe config with Spring records

configuration validation records
Intermediate 6 steps
ruby 
module SoftDeletable
  extend ActiveSupport::Concern
 
  included do

How a soft-delete concern works in Rails

concerns soft-delete scopes
Intermediate 8 steps
typescript 
type CloneInput = Record<string, unknown> | unknown[] | Map<unknown, unknown> | Set<unknown>;
 
export function deepClone<T>(value: T): T {
  if (typeof structuredClone === "function") {

Building a deepClone with cycle safety

recursion deep-copy cycle-detection
Intermediate 8 steps
rust 
use std::fs::File;
use std::io::{self, BufRead, BufReader};
use std::path::Path;
 

Buffered log scanning in Rust

buffered-io error-handling streaming
Intermediate 9 steps
python 
from functools import wraps
 
 
def memoize(func):

Building a memoize decorator in Python

decorators closures memoization
Intermediate 5 steps
php 
<?php
 
namespace App\Support;
 

Grouping records with array_reduce in PHP

array-reduce grouping higher-order-functions
Intermediate 6 steps
java 
@Component
public class RequestTimingInterceptor implements HandlerInterceptor {
 
    private static final Logger log = LoggerFactory.getLogger(RequestTimingInterceptor.class);

How a Spring HandlerInterceptor times requests

interceptor request-lifecycle logging
Intermediate 6 steps
ruby 
class Post < ApplicationRecord
  before_validation :generate_slug, on: :create
 
  validates :slug, presence: true, uniqueness: true

How a Rails model builds unique slugs

slugs callbacks validations
Intermediate 7 steps
go 
package middleware
 
import (
	"errors"

Centralized error handling in Gin

middleware error-handling custom-errors
Intermediate 8 steps
typescript 
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable, shareReplay } from 'rxjs';
 

Caching HTTP config in an Angular service

caching observables dependency-injection
Intermediate 6 steps
rust 
use axum::{
    extract::{Path, State},
    routing::{get, post},
    Json, Router,

Building a nested REST API router in Axum

routing extractors shared-state
Intermediate 8 steps
python 
import os
import tempfile
from pathlib import Path
from typing import Union

How atomic file writes work in Python

atomicity filesystem durability
Advanced 7 steps
php 
<?php
 
namespace App\Console;
 

How task scheduling works in Laravel

scheduling cron fluent-api
Intermediate 7 steps
javascript 
import { useState, useEffect } from "react";
 
export function useUser(userId) {
  const [user, setUser] = useState(null);

How a data-fetching hook works in React

custom-hooks data-fetching abortcontroller
Intermediate 8 steps
php 
<?php
 
namespace App\Policies;
 

How authorization policies gate updates in Laravel

authorization policies access control
Intermediate 7 steps
typescript 
import {
  CACHE_MANAGER,
  CacheInterceptor,
} from '@nestjs/cache-manager';

A tenant-aware HTTP cache in NestJS

caching interceptors multi-tenancy
Intermediate 7 steps
java 
@RestController
@RequestMapping("/api/products")
public class ProductController {
 

How a paginated REST controller works in Spring

pagination dto-mapping dependency-injection
Intermediate 8 steps