Code Explainers

Browse the library

php 
<?php
 
namespace App\FeatureFlags;
 

How a feature flag evaluator decides

feature-flags rollout hashing
Intermediate 8 steps
go 
type CreateUserInput struct {
	Name     string `json:"name" binding:"required,min=2,max=64"`
	Email    string `json:"email" binding:"required,email"`
	Password string `json:"password" binding:"required,min=8"`

Turning Gin validation errors into JSON

validation request-binding error-handling
Intermediate 9 steps
javascript 
const express = require('express');
const { createProxyMiddleware, fixRequestBody } = require('http-proxy-middleware');
 
const router = express.Router();

Building an API gateway proxy in Express

reverse-proxy middleware api-gateway
Intermediate 6 steps
rust 
use axum::{
    extract::{FromRequestParts, Query},
    http::{request::Parts, StatusCode},
};

Building a custom Axum extractor for query filters

extractors query-parsing enums
Intermediate 8 steps
go 
package middleware
 
import (
	"net/http"

Per-IP write rate limiting in Gin

rate-limiting middleware concurrency
Intermediate 8 steps
typescript 
import { Injectable, signal, computed, effect, inject } from '@angular/core';
import { DOCUMENT } from '@angular/common';
 
export type Theme = 'light' | 'dark';

A signal-based theme service in Angular

signals reactivity dependency-injection
Intermediate 7 steps
python 
import asyncio
from dataclasses import dataclass
 
import aiohttp

Bounded-concurrency HTTP fetching with asyncio

async concurrency semaphore
Intermediate 8 steps
php 
namespace App\Providers;
 
use Illuminate\Support\Facades\Blade;
use Illuminate\Support\ServiceProvider;

Building a @money Blade directive in Laravel

blade-directive service-provider localization
Intermediate 5 steps
javascript 
import { useCallback, useRef, useState } from 'react';
 
export function ColorPicker({ initialColor = '#3b82f6', onCommit }) {
  const [committed, setCommitted] = useState(initialColor);

A validated color picker in React

uncontrolled-inputs refs validation
Intermediate 7 steps
rust 
use std::sync::Arc;
use axum::{
    extract::{Multipart, State},
    http::StatusCode,

Throttling file uploads in Axum with a Semaphore

concurrency backpressure multipart
Advanced 8 steps
go 
package middleware
 
import (
	"net/http"

A content-type guard middleware in Gin

middleware closures http
Intermediate 7 steps
typescript 
import { Injectable } from '@angular/core';
import { HttpClient, HttpEventType, HttpRequest } from '@angular/common/http';
import { Observable } from 'rxjs';
import { map, distinctUntilChanged, scan } from 'rxjs/operators';

Tracking upload progress in Angular

rxjs http-events state-reduction
Intermediate 8 steps
python 
from pathlib import Path
from typing import Iterator
 
 

Filtering files with pathlib.glob

generators filesystem filtering
Intermediate 6 steps
php 
<?php
 
namespace App\Queue;
 

Deduplicating a job queue with Redis

deduplication redis atomicity
Advanced 8 steps
javascript 
import { useEffect, useRef } from 'react';
 
export function useRefetchOnFocus(refetch, { staleTime = 30_000 } = {}) {
  const lastFetchedAt = useRef(Date.now());

A React hook that refetches on tab focus

custom-hooks refs event-listeners
Intermediate 6 steps
rust 
use once_cell::sync::Lazy;
use regex::Regex;
 
static NON_ALPHANUMERIC: Lazy<Regex> = Lazy::new(|| Regex::new(r"[^a-z0-9]+").unwrap());

Building URL slugs in Rust

string-processing regex transliteration
Intermediate 8 steps
go 
package api
 
import (
	"errors"

Turning Gin validation errors into JSON

validation error-handling http-handlers
Intermediate 9 steps
java 
public final class CaseConverter {
 
    private static final Pattern CAMEL_BOUNDARY =
            Pattern.compile("([a-z0-9])([A-Z])|([A-Z]+)([A-Z][a-z])");

Converting camelCase to snake_case in Java

regex string-manipulation utility-class
Intermediate 7 steps