Code Explainers

Browse the library

javascript 
const express = require('express');
const multer = require('multer');
const path = require('path');
const crypto = require('crypto');

Safe image uploads with Multer in Express

file-upload multer validation
Intermediate 7 steps
go 
type PostCursor struct {
	CreatedAt time.Time
	ID        int64
}

Keyset pagination with cursors in Go

pagination keyset-cursor database
Intermediate 8 steps
java 
@Configuration
@EnableWebSecurity
public class ResourceServerConfig {
 

Configuring a JWT resource server in Spring

oauth2 jwt authorization
Intermediate 8 steps
ruby 
require "openssl"
require "json"
require "base64"
 

Building signed session tokens in Ruby

hmac authentication cryptography
Intermediate 8 steps
php 
<?php
 
namespace App\Http\Requests;
 

A validated date-range value object in PHP

value-object validation immutability
Intermediate 7 steps
python 
import wave
import os
from dataclasses import dataclass
 

Reading WAV metadata into a dataclass

dataclass audio file-io
Beginner 5 steps
rust 
use std::collections::VecDeque;
 
#[derive(Debug)]
pub struct Hunk {

Applying a diff hunk in Rust

enums error-handling pattern-matching
Intermediate 8 steps
typescript 
import { Component, input, computed } from '@angular/core';
 
function toNumber(value: number | string): number {
  return typeof value === 'number' ? value : parseFloat(value);

Signal inputs and computed in Angular

signals reactivity derived-state
Intermediate 5 steps
javascript 
const express = require('express');
const jwt = require('jsonwebtoken');
const crypto = require('crypto');
 

Refresh token rotation in Express

jwt token-rotation authentication
Advanced 9 steps
go 
package config
 
import (
	"fmt"

Parsing timeout config in Go

configuration validation error-wrapping
Intermediate 7 steps
java 
@Configuration
public class OrderConsumerConfig {
 
    @Bean

Wiring a resilient Kafka consumer in Spring

kafka deserialization error-handling
Intermediate 8 steps
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