Code Explainers

Browse the library

ruby 
class Product < ApplicationRecord
  belongs_to :category, touch: true
 
  has_many :reviews, dependent: :destroy

How Rails models wire up associations

active record associations validations
Intermediate 7 steps
typescript 
import sanitizeHtml from "sanitize-html";
 
interface RichTextOptions {
  allowImages?: boolean;

Building a configurable HTML sanitizer allowlist

sanitization xss-prevention allowlist
Intermediate 7 steps
go 
func (h *WebhookHandler) HandleBatch(c *gin.Context) {
	var payload BatchWebhookPayload
	if err := c.ShouldBindJSON(&payload); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid payload"})

Handling batched webhooks in Gin

webhooks signature-verification job-queue
Intermediate 7 steps
ruby 
require "net/http"
require "json"
require "uri"
require "base64"

Paginating an HTTP API with a Ruby enumerator

pagination http enumerator
Intermediate 7 steps
javascript 
class StarRating {
  constructor(container, { max = 5, value = 0, onChange } = {}) {
    this.container = container;
    this.max = max;

Building an accessible star-rating widget

dom event-handling accessibility
Intermediate 7 steps
python 
from pathlib import Path
from collections import defaultdict
 
from PIL import Image

Finding near-duplicate images by perceptual hash

perceptual-hashing clustering hamming-distance
Intermediate 9 steps
rust 
use axum::{
    body::Body,
    http::{Method, StatusCode, Uri},
    response::{IntoResponse, Response},

Nesting routers and JSON fallbacks in Axum

routing http json-responses
Intermediate 7 steps
java 
@Configuration
@EnableKafka
public class KafkaErrorHandlingConfig {
 

Kafka retry and dead-letter handling in Spring

kafka error-handling retry
Intermediate 7 steps
php 
<?php
 
namespace App\Http\Controllers\Api;
 

Building a cursor-paginated feed in Laravel

cursor-pagination eager-loading validation
Intermediate 8 steps
typescript 
import { useCallback, useEffect, useRef, useState } from "react";
 
interface Page<T> {
  items: T[];

A cursor-based infinite scroll hook in React

custom-hooks pagination intersection-observer
Intermediate 9 steps
go 
package config
 
import "time"
 

The functional options pattern in Go

functional-options closures immutability
Intermediate 7 steps
ruby 
class DateRangeMerger
  def initialize(ranges)
    @ranges = ranges
  end

Merging overlapping date ranges in Ruby

sorting interval-merging enumerable
Intermediate 5 steps
javascript 
const form = document.querySelector('#signup-form');
const password = form.querySelector('#password');
const confirm = form.querySelector('#confirm-password');
const submit = form.querySelector('button[type="submit"]');

Live password-match validation in the DOM

form-validation dom-events accessibility
Intermediate 6 steps
python 
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request
from starlette.responses import JSONResponse, Response
from starlette.status import HTTP_413_REQUEST_ENTITY_TOO_LARGE

Enforcing a max request body size in FastAPI

middleware streaming request-limits
Advanced 6 steps
rust 
use axum::{
    extract::FromRequestParts,
    http::{request::Parts, StatusCode, header::ACCEPT_LANGUAGE},
};

A locale extractor for Axum handlers

content-negotiation http-headers custom-extractor
Intermediate 7 steps
java 
@Controller
@RequestMapping("/employees")
public class EmployeeController {
 

Customizing form binding in a Spring MVC controller

data-binding validation type-conversion
Intermediate 9 steps
php 
<?php
 
namespace App\Services;
 

Caching per-tenant settings in Laravel

caching multi-tenancy dependency-injection
Intermediate 7 steps
typescript 
type NestedValue = string | NestedValue[] | { [key: string]: NestedValue };
 
function parseFieldPath(name: string): string[] {
  const match = name.match(/^([^\[\]]+)((?:\[[^\[\]]*\])*)$/);

Parsing bracketed form field names into nested objects

parsing recursive-types regex
Intermediate 8 steps