Intermediate code explainers

ruby

class WeeklySignupsReport
  DEFAULT_WEEKS = 12
 
  def initialize(weeks: DEFAULT_WEEKS, source: User.all)

Building a weekly signups report in Rails

service object aggregation group by

Intermediate 7 steps

python

import random
from typing import Iterator, List

How reservoir sampling picks k items

reservoir-sampling streaming randomness

Intermediate 5 steps

php

<?php
 
namespace App\Services;

Building a cached daily leaderboard in Laravel

caching aggregation eager-loading

Intermediate 9 steps

rust

use chrono::{Duration, NaiveDate};
 
#[derive(Debug)]
pub struct DateRange {

Parsing and iterating date ranges in Rust

error-handling iterators parsing

Intermediate 7 steps

java

public static Map<String, String> parseCookieHeader(String header) {
    Map<String, String> cookies = new LinkedHashMap<>();
    if (header == null || header.isBlank()) {
        return cookies;

Parsing an HTTP Cookie header in Java

string-parsing http url-decoding

Intermediate 6 steps

typescript

import { useEffect, useState } from "react";
 
interface Section {
  id: string;

Building a scroll-spy hook in React

custom-hooks intersectionobserver dom-observation

Intermediate 8 steps

go

package logging
 
import (
	"context"

Deduplicating log attributes in Go's slog

decorator-pattern structured-logging immutability

Intermediate 8 steps

ruby

class ApplicationController < ActionController::Base
  EXPERIMENTS = {
    checkout_button_color: %w[control blue green],
    onboarding_flow: %w[control streamlined]

How A/B test cohorts are assigned in Rails

a-b-testing cookies hashing

Intermediate 8 steps

python

import secrets
 
from django.contrib.auth import authenticate, login
from django.core.cache import cache

Two-factor login with OTP in Django

two-factor-auth one-time-passwords caching

Intermediate 9 steps

php

<?php
 
final class RotatingFileLogger
{

How a rotating file logger works in PHP

logging file-rotation io

Intermediate 9 steps

java

public class TimedSocketReader {
 
    private static final int READ_TIMEOUT_MS = 5_000;
    private static final int CONNECT_TIMEOUT_MS = 3_000;

Reading a socket with connect and read timeouts

sockets timeouts io

Intermediate 8 steps

javascript

import { useEffect, useRef, useState } from 'react';
 
export function useDelayedFlag(active, delay = 300) {
  const [visible, setVisible] = useState(false);

Delaying a loading spinner with a React hook

custom-hooks debouncing cleanup

Intermediate 8 steps

go

package middleware
 
import (
	"net/http"

Per-plan export limits in Gin middleware

middleware rate-limiting authorization

Intermediate 7 steps

ruby

class SnippetHighlighter
  CONTEXT_RADIUS = 60
  MAX_TERMS = 8

Building search-result snippets in Ruby

regular-expressions text-processing search

Intermediate 9 steps

python

import re
from functools import total_ordering
from typing import Optional

Parsing and comparing semantic versions

regex operator-overloading sorting

Intermediate 7 steps

javascript

const SWIPE_THRESHOLD = 80;
const MAX_TRANSLATE = 120;
 
export function attachSwipeToDismiss(element, onDismiss) {

Building a swipe-to-dismiss gesture in JS

touch-events gesture-detection dom-manipulation

Intermediate 10 steps

rust

use axum::{
    async_trait,
    extract::{rejection::JsonRejection, FromRequest, Request},
    http::StatusCode,

A validated JSON extractor in Axum

extractors validation error-handling

Intermediate 8 steps

java

public final class EncodingDetector {
 
    public enum Encoding {
        UTF_8, UTF_16LE, UTF_16BE, UTF_32LE, UTF_32BE, ASCII, UNKNOWN

Detecting text encoding from raw bytes in Java

byte-manipulation encoding-detection bitwise-operations

Intermediate 8 steps