Code Explainers

Browse the library

typescript 
interface JwtPayload {
  exp?: number;
  iat?: number;
  sub?: string;

Decoding a JWT to check expiry

jwt base64url type-guards
Intermediate 8 steps
go 
package logbuffer
 
import (
	"bufio"

A buffered logger with background flushing in Go

concurrency buffering context
Intermediate 8 steps
python 
from urllib.parse import urlparse
 
 
class RobotsRules:

Parsing and applying a robots.txt file

parsing longest-prefix-match state-machine
Intermediate 10 steps
rust 
use std::net::{IpAddr, SocketAddr};
 
use axum::extract::{ConnectInfo, FromRequestParts};
use axum::http::request::Parts;

How a custom ClientIp extractor works in Axum

extractor http-headers proxy-forwarding
Intermediate 8 steps
java 
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Currency;
 

A safe Money value type in Java

immutability bigdecimal value-object
Intermediate 10 steps
javascript 
'use client';
 
import { useRouter } from 'next/navigation';
import Link from 'next/link';

Archiving with router.refresh in Next.js

client-component data-mutation transitions
Intermediate 7 steps
ruby 
class ThumbnailPool
  def initialize(worker_count: 4, capacity: 100)
    @queue = SizedQueue.new(capacity)
    @running = true

A thread pool for thumbnail jobs in Ruby

concurrency thread-pool bounded-queue
Advanced 7 steps
php 
<?php
 
namespace App\Providers;
 

Defining feature flags with Laravel Pennant

feature-flags service-provider config-driven
Intermediate 6 steps
typescript 
import { Directive, EventEmitter, HostListener, Input, Output } from '@angular/core';
 
interface Shortcut {
  key: string;

A keyboard shortcut directive in Angular

directives event-handling keyboard-shortcuts
Intermediate 9 steps
go 
package handler
 
import (
	"net/http"

Custom time validation in Gin

validation request-binding struct-tags
Intermediate 8 steps
python 
from pathlib import Path
 
from django.contrib.auth.decorators import login_required
from django.http import FileResponse, Http404, HttpResponseForbidden

Serving files with access checks in Django

authorization http-caching file-serving
Intermediate 7 steps
rust 
use once_cell::sync::Lazy;
use regex::Regex;
 
static LOG_LINE: Lazy<Regex> = Lazy::new(|| {

Parsing access logs with a lazy regex in Rust

regex lazy-initialization parsing
Intermediate 7 steps
java 
public class RequestCoalescer<K, V> {
 
    private final ConcurrentHashMap<K, CompletableFuture<V>> inFlight = new ConcurrentHashMap<>();
    private final Function<K, V> loader;

Coalescing duplicate requests in Java

concurrency caching completablefuture
Advanced 6 steps
javascript 
import { useState, useRef, useCallback } from "react";
 
export function MultiSelect({ options, value, onChange, placeholder = "Select…" }) {
  const [open, setOpen] = useState(false);

Building a keyboard-accessible MultiSelect in React

controlled-component accessibility keyboard-navigation
Intermediate 10 steps
java 
public final class NaturalOrderComparator implements Comparator<String> {
 
    public static final NaturalOrderComparator INSTANCE = new NaturalOrderComparator();
 

Natural-order string sorting in Java

comparator natural-sort string-parsing
Intermediate 9 steps
rust 
use axum::{
    extract::State,
    response::sse::{Event, KeepAlive, Sse},
    Json,

Proxying an SSE chat stream in Axum

server-sent-events streaming async-generators
Advanced 10 steps
go 
package middleware
 
import (
	"net/http"

Localized validation errors in Gin

middleware internationalization validation
Intermediate 8 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Email confirmation with signed URLs in Laravel

signed-urls email-verification middleware
Intermediate 6 steps