Code Explainers

Browse the library

typescript 
import { useCallback, useEffect, useRef, useState } from "react";
 
interface UseResendCooldownOptions {
  cooldownSeconds?: number;

A resend cooldown hook in React

custom-hooks timers state-management
Intermediate 7 steps
go 
package events
 
import (
	"net/http"

Two-pass JSON dispatch in Gin

polymorphic-json request-binding validation
Intermediate 8 steps
ruby 
class HashDiff
  Change = Struct.new(:from, :to)
 
  def self.call(before, after)

Diffing two hashes in Ruby

set-operations struct enumerable
Intermediate 7 steps
php 
final class FieldEncryptor
{
    private string $key;
 

Authenticated field encryption with libsodium

encryption libsodium authenticated-encryption
Intermediate 7 steps
javascript 
const FOCUSABLE = [
  'a[href]',
  'button:not([disabled])',
  'input:not([disabled])',

How to trap keyboard focus in a dialog

accessibility dom event-handling
Intermediate 8 steps
java 
package com.example.uploads.config;
 
import jakarta.servlet.MultipartConfigElement;
import org.springframework.boot.web.servlet.MultipartConfigFactory;

Configuring upload size limits in Spring

file-upload exception-handling http-errors
Intermediate 6 steps
python 
import datetime
from dataclasses import dataclass
 
 

Parsing fixed-width records in Python

parsing generators dataclasses
Intermediate 8 steps
typescript 
import {
  Injectable,
  PipeTransform,
  ArgumentMetadata,

A custom validation pipe in NestJS

validation dto recursion
Intermediate 10 steps
ruby 
module CreditCard
  module_function
 
  def valid?(number)

Validating credit card numbers with Luhn

checksum luhn-algorithm validation
Intermediate 6 steps
go 
package handlers
 
type ListFilters struct {
	Status    string `form:"status" binding:"omitempty,oneof=active archived all"`

Cross-field query validation in Gin

validation struct-tags query-binding
Intermediate 9 steps
javascript 
function generateCalendarGrid(year, month) {
  const firstDay = new Date(year, month, 1);
  const lastDay = new Date(year, month + 1, 0);
  const daysInMonth = lastDay.getDate();

Building a text calendar in JavaScript

date-handling grid-layout modular-arithmetic
Intermediate 9 steps
rust 
use std::collections::HashMap;
 
#[derive(Debug)]
pub struct RequestHead {

Parsing an HTTP request head in Rust

parsing error-handling iterators
Intermediate 9 steps
php 
<?php
 
final class MarkdownParser
{

Building a small Markdown-to-HTML parser in PHP

state-machine parsing closures
Intermediate 10 steps
java 
public final class Levenshtein {
 
    private Levenshtein() {
    }

Two-row Levenshtein distance in Java

dynamic-programming edit-distance space-optimization
Intermediate 8 steps
python 
from itertools import product
from dataclasses import dataclass
from decimal import Decimal
 

Generating product variants with itertools.product

cartesian-product dataclass decimal
Intermediate 7 steps
typescript 
import {
  CallHandler,
  ExecutionContext,
  Injectable,

Recording HTTP metrics with a NestJS interceptor

interceptor observability prometheus
Intermediate 5 steps
ruby 
class UserColor
  GOLDEN_RATIO_CONJUGATE = 0.618033988749895
 
  def initialize(username)

Deriving a stable color from a username

hashing color-theory deterministic-mapping
Intermediate 7 steps
go 
package editor
 
import (
	"context"

How a debouncer coalesces bursts in Go

debounce concurrency timers
Intermediate 8 steps