Intermediate code explainers

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

javascript

function initScrollSpy() {
  const links = Array.from(document.querySelectorAll('.nav a[href^="#"]'));
  const sections = links
    .map((link) => document.querySelector(link.getAttribute('href')))

Building a scroll spy with IntersectionObserver

intersectionobserver dom event-driven

Intermediate 7 steps

rust

#[derive(Debug, Default)]
pub struct RequestBuilder {
    url: String,
    method: String,

The builder pattern in Rust

builder-pattern method-chaining ergonomic-api

Intermediate 8 steps

java

package com.example.lb;
 
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

A thread-safe round-robin load balancer in Java

concurrency load-balancing round-robin

Intermediate 9 steps

python

from typing import Callable, Dict, Type
 
 
class PluginRegistry:

A decorator-based plugin registry in Python

decorators registry pattern factory

Intermediate 9 steps

ruby

namespace :counter_cache do
  desc "Recalculate comments_count for posts after a backfill"
  task warm_post_comments: :environment do
    scope = Post.where(comments_count: nil).or(Post.where("comments_count < 0"))

Backfilling counter caches in a Rake task in Rails

counter-cache batching rake-tasks

Intermediate 6 steps

go

package humanize
 
import (
	"fmt"

Parsing human-readable byte sizes in Go

parsing regex lookup-table

Intermediate 8 steps

ruby

class ToastBroadcaster
  include ActionView::RecordIdentifier
 
  def self.broadcast_to(user, message:, type: :notice)

How Turbo Stream toasts broadcast in Rails

turbo-streams service-object real-time

Intermediate 6 steps