Code Explainers

Browse the library

rust 
use axum::{
    extract::FromRequestParts,
    http::{request::Parts, StatusCode, header::AUTHORIZATION},
};

How a JWT extractor works in Axum

authentication jwt extractors
Intermediate 8 steps
javascript 
import { useMemo, useState } from 'react';
 
function ProductList({ products }) {
  const [query, setQuery] = useState('');

Memoizing a filtered list in React

memoization derived-state filtering
Intermediate 8 steps
ruby 
module Fibonacci
  CACHE = Hash.new do |cache, n|
    cache[n] = cache[n - 1] + cache[n - 2]
  end

Memoizing Fibonacci with a Hash default block

memoization recursion hash-default
Intermediate 5 steps
go 
package retry
 
import (
	"context"

Retry with exponential backoff in Go

retry exponential-backoff jitter
Intermediate 8 steps
typescript 
type SignupInput = {
  email: string;
  password: string;
  confirmPassword: string;

How a typed signup validator collects errors

form-validation type-safety regex
Intermediate 9 steps
java 
public final class BusinessDays {
 
    private BusinessDays() {
    }

Counting business days between two dates in Java

date arithmetic utility class streams
Intermediate 7 steps
python 
import hashlib
import hmac
import os
 

Verifying signed payment webhooks in Flask

hmac webhooks signature verification
Intermediate 7 steps
php 
<?php
 
final class CsrfGuard
{

Building a per-form CSRF guard in PHP

csrf security sessions
Intermediate 8 steps
php 
<?php
 
namespace App\Models;
 

Polymorphic comments in Laravel with morphTo

polymorphism eloquent relationships
Intermediate 5 steps
java 
import java.time.Duration;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;

A safe recurring heartbeat scheduler in Java

concurrency scheduling thread-safety
Intermediate 6 steps
javascript 
function initLazyLoad(root = document) {
  const images = root.querySelectorAll('img[data-src]');
 
  if (!('IntersectionObserver' in window)) {

How lazy image loading works

lazy-loading intersectionobserver progressive-enhancement
Intermediate 8 steps
go 
package main
 
import (
	"bufio"

Counting matching lines in Go with bufio

file-io buffered-scanning error-handling
Intermediate 4 steps
ruby 
class EventEmitter
  def initialize
    @listeners = Hash.new { |hash, key| hash[key] = [] }
  end

Building an EventEmitter in Ruby

pub-sub closures callbacks
Intermediate 7 steps
python 
from flask import Blueprint, render_template, request, abort
from sqlalchemy import select
 
from .models import Article

Paginating articles in a Flask Blueprint

pagination blueprints input-validation
Intermediate 6 steps
javascript 
import { notFound } from 'next/navigation';
 
const PER_PAGE = 24;
const SORT_OPTIONS = ['relevance', 'price-asc', 'price-desc', 'newest'];

Parsing search params in a Next.js page

input-validation query-params pagination
Intermediate 10 steps
go 
package collection
 
func Deduplicate[T comparable](items []T) []T {
	seen := make(map[T]struct{}, len(items))

Generic deduplication in Go

generics deduplication maps
Intermediate 5 steps
ruby 
require 'optparse'
require 'ostruct'
 
def parse_options(argv)

Parsing CLI options with OptionParser

cli argument-parsing validation
Intermediate 8 steps
rust 
use axum::{extract::Form, http::StatusCode, response::{IntoResponse, Response}, Json};
use serde::Deserialize;
use serde_json::json;
use std::collections::HashMap;

Validating a signup form in Axum

form-validation deserialization error-handling
Intermediate 8 steps