Code Explainers

Browse the library

typescript 
type RGB = readonly [number, number, number];
 
interface ColorStop {
  offset: number;

Interpolating a color gradient in TypeScript

interpolation data-visualization color
Intermediate 8 steps
php 
final class FormEditorHistory
{
    private SplStack $undoStack;
    private SplStack $redoStack;

Undo/redo with two stacks in PHP

undo-redo stack state-management
Intermediate 9 steps
go 
package api
 
import (
	"encoding/json"

Safely decoding JSON in a Go HTTP handler

http json-decoding input-validation
Intermediate 8 steps
java 
public final class ThrottledLogger {
 
    private final Logger delegate;
    private final long windowMillis;

Rate-limiting log spam with per-message windows

concurrency rate-limiting throttling
Advanced 8 steps
php 
<?php
 
namespace App\Reports;
 

Bucketing spending by time period in Laravel

aggregation date-bucketing collections
Intermediate 9 steps
javascript 
'use client';
 
import { useActionState } from 'react';
import { submitSignup } from './actions';

Multi-step forms with useActionState in Next.js

server-actions form-state progressive-enhancement
Intermediate 10 steps
rust 
use axum::{
    body::Body,
    extract::Request,
    http::{header, StatusCode},

A CSRF verification middleware in Axum

csrf middleware security
Intermediate 10 steps
python 
import hashlib
import json
from functools import wraps
from flask import g, request, jsonify, current_app

Building an idempotency decorator in Flask

idempotency decorators redis
Advanced 7 steps
typescript 
import { useCallback, useId, useRef, useState, type KeyboardEvent } from 'react';
 
interface Tab {
  id: string;

Building an accessible tabs component in React

accessibility aria keyboard-navigation
Intermediate 8 steps
java 
public final class MapFlattener {
 
    private MapFlattener() {
    }

Flattening nested maps into dotted keys

recursion tree-traversal data-transformation
Intermediate 7 steps
php 
<?php
 
namespace App\Http\Controllers;
 

Conditional query building in Laravel

query-builder conditional-logic closures
Intermediate 7 steps
javascript 
import { notFound } from 'next/navigation'
import { getPhotoById } from '@/lib/photos'
import Modal from '@/components/modal'
import Image from 'next/image'

An intercepted photo modal route in Next.js

dynamic-routes async-components metadata
Intermediate 6 steps
ruby 
def wrap_text(text, width = 80)
  raise ArgumentError, "width must be positive" unless width.positive?
 
  text.split(/\n/, -1).map do |paragraph|

How greedy text wrapping works in Ruby

string-processing greedy-algorithm text-wrapping
Intermediate 7 steps
rust 
pub fn extract_quoted_fields(line: &str) -> Vec<String> {
    let mut fields = Vec::new();
    let mut current = String::new();
    let mut in_quotes = false;

Parsing quoted fields with a state machine in Rust

state-machine parsing string-processing
Intermediate 7 steps
python 
from flask import Flask, request, redirect, current_app
from werkzeug.middleware.proxy_fix import ProxyFix
 
app = Flask(__name__)

Enforcing HTTPS behind a proxy in Flask

https middleware security-headers
Intermediate 7 steps
typescript 
import {
  CallHandler,
  ConflictException,
  ExecutionContext,

Idempotent POST requests in NestJS with Redis

idempotency interceptor redis
Advanced 7 steps
java 
package com.example.actuator;
 
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.actuate.endpoint.annotation.Endpoint;

Building a custom Spring Boot Actuator endpoint

actuator dependency-injection observability
Intermediate 7 steps
php 
<?php
 
namespace App\Notifications;
 

Delayed, self-cancelling emails in Laravel

queues notifications delayed-jobs
Intermediate 7 steps