Code Explainers

Browse the library

php 
<?php
 
class ImageUploadService
{

Validating file uploads safely in PHP

file-upload input-validation security
Intermediate 8 steps
ruby 
class Comment < ApplicationRecord
  belongs_to :post
  belongs_to :author, class_name: "User"
 

Live-updating comments with Turbo in Rails

turbo-streams callbacks associations
Intermediate 8 steps
python 
import time
from collections import defaultdict
from threading import Lock
 

Sliding-window login rate limiting in Flask

rate-limiting sliding-window thread-safety
Intermediate 7 steps
rust 
use std::time::Instant;
use tracing::info;
 
pub struct Timer {

A scope-guard timer with Drop in Rust

raii drop-guard timing
Intermediate 7 steps
javascript 
const RATE_LIMIT = 100;
const WINDOW_MS = 60 * 1000;
const BLOCK_MS = 5 * 60 * 1000;
 

Building a rate-limiting middleware in Express

rate-limiting middleware closures
Intermediate 9 steps
go 
package model
 
import (
	"encoding/json"

Custom JSON marshaling in Go

json serialization interfaces
Intermediate 5 steps
java 
import java.util.ArrayDeque;
import java.util.Deque;
 
public final class RollingAverage {

A rolling average over a sliding window

sliding-window running-sum deque
Intermediate 7 steps
typescript 
const DIVISIONS: { amount: number; unit: Intl.RelativeTimeFormatUnit }[] = [
  { amount: 60, unit: "seconds" },
  { amount: 60, unit: "minutes" },
  { amount: 24, unit: "hours" },

Human-readable relative times with Intl

internationalization date-formatting lookup-table
Intermediate 7 steps
php 
<?php
 
namespace App\View;
 

Building a safe HTML escaper in PHP

security xss escaping
Intermediate 6 steps
ruby 
require 'json'
require 'set'
 
class SensitiveScrubber

Recursively scrubbing secrets from JSON

recursion data-masking pattern-matching
Intermediate 7 steps
python 
from django.conf import settings
from django.contrib.auth import get_user_model
from django.core.mail import EmailMultiAlternatives
from django.db.models.signals import post_save

Sending a welcome email with Django signals

signals email user-activation
Intermediate 8 steps
rust 
use std::collections::HashMap;
 
pub struct Memoizer<K, V, F> {
    cache: HashMap<K, V>,

A generic memoizer in Rust

memoization generics caching
Intermediate 6 steps
javascript 
const transitions = {
  cart: { checkout: 'shipping' },
  shipping: { submitAddress: 'payment', back: 'cart' },
  payment: { submitPayment: 'review', back: 'shipping' },

A finite state machine for checkout flow

state-machine event-driven data-driven-design
Intermediate 7 steps
java 
@Target({ElementType.FIELD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = StrongPasswordValidator.class)
@Documented

Building a custom @StrongPassword validator in Spring

bean-validation annotations regex
Intermediate 7 steps
typescript 
import { Component } from '@angular/core';
import { FormControl, ReactiveFormsModule } from '@angular/forms';
import { HttpClient } from '@angular/common/http';
import { AsyncPipe } from '@angular/common';

Reactive type-ahead search in Angular

rxjs reactive-forms debounce
Intermediate 9 steps
php 
<?php
 
namespace App\Observers;
 

How Eloquent observers hook lifecycle events in Laravel

observers lifecycle-hooks queues
Intermediate 6 steps
ruby 
class ReportBatcher
  BATCH_SIZE = 500
 
  def initialize(account)

Batching monthly email summaries in Rails

batching service-object background-jobs
Intermediate 7 steps
python 
import csv
import io
from datetime import date
 

Streaming a CSV export in FastAPI

streaming async-generators csv
Advanced 8 steps