Code Explainers

Browse the library

javascript 
import { useEffect, useRef, useState } from 'react';
 
export function useDelayedFlag(active, delay = 300) {
  const [visible, setVisible] = useState(false);

Delaying a loading spinner with a React hook

custom-hooks debouncing cleanup
Intermediate 8 steps
go 
package middleware
 
import (
	"net/http"

Per-plan export limits in Gin middleware

middleware rate-limiting authorization
Intermediate 7 steps
ruby 
class SnippetHighlighter
  CONTEXT_RADIUS = 60
  MAX_TERMS = 8
 

Building search-result snippets in Ruby

regular-expressions text-processing search
Intermediate 9 steps
python 
import re
from functools import total_ordering
from typing import Optional
 

Parsing and comparing semantic versions

regex operator-overloading sorting
Intermediate 7 steps
javascript 
const SWIPE_THRESHOLD = 80;
const MAX_TRANSLATE = 120;
 
export function attachSwipeToDismiss(element, onDismiss) {

Building a swipe-to-dismiss gesture in JS

touch-events gesture-detection dom-manipulation
Intermediate 10 steps
rust 
use axum::{
    async_trait,
    extract::{rejection::JsonRejection, FromRequest, Request},
    http::StatusCode,

A validated JSON extractor in Axum

extractors validation error-handling
Intermediate 8 steps
java 
public final class EncodingDetector {
 
    public enum Encoding {
        UTF_8, UTF_16LE, UTF_16BE, UTF_32LE, UTF_32BE, ASCII, UNKNOWN

Detecting text encoding from raw bytes in Java

byte-manipulation encoding-detection bitwise-operations
Intermediate 8 steps
go 
package httputil
 
import (
	"net"

Safely extracting the real client IP in Go

security http ip-spoofing
Intermediate 7 steps
ruby 
require "openssl"
require "base32"
 
class TOTP

How TOTP one-time codes work in Ruby

hmac authentication totp
Intermediate 7 steps
python 
from typing import Any, Sequence, Mapping
 
 
def render_markdown_table(

Rendering an aligned Markdown table in Python

string formatting data transformation closures
Intermediate 8 steps
rust 
use std::time::Duration;
use tokio::sync::mpsc;
use tokio::time::{interval, MissedTickBehavior};
 

A token-bucket rate limiter in Tokio

rate-limiting channels async
Advanced 8 steps
php 
class TwoFactorController extends Controller
{
    public function show(Request $request): View|RedirectResponse
    {

Two-factor auth challenge flow in Laravel

authentication two-factor middleware
Intermediate 10 steps
java 
public final class ImportOrganizer {
 
    private static final Pattern IMPORT_LINE =
            Pattern.compile("^import\\s+(static\\s+)?([\\w.]+(?:\\.\\*)?)\\s*;\\s*$");

Sorting Java imports with a regex pass

regex sorting text-processing
Intermediate 8 steps
typescript 
import { Pipe, PipeTransform } from '@angular/core';
 
@Pipe({
  name: 'chunk',

A memoized chunk pipe in Angular

memoization weakmap pure-pipes
Intermediate 7 steps
go 
package signup
 
var wizardCodec = securecookie.New(
	[]byte(os.Getenv("WIZARD_HASH_KEY")),

A cookie-backed signup wizard in Gin

cookies encryption multi-step-form
Intermediate 9 steps
ruby 
class Coupon < ApplicationRecord
  has_many :redemptions, dependent: :destroy
 
  validates :code, presence: true, uniqueness: { case_sensitive: false }

Safe coupon redemption in Rails

validation contexts pessimistic locking scopes
Advanced 10 steps
python 
from django.db import connections
from django.db.utils import OperationalError
from django.core.cache import caches
from django.http import JsonResponse

Building a health check endpoint in Django

health check monitoring database
Intermediate 7 steps
javascript 
const { pool } = require('./db');
 
function withTransaction() {
  return async (req, res, next) => {

A per-request transaction middleware in Express

middleware database-transactions connection-pooling
Advanced 7 steps