Intermediate code explainers

java

package com.example.web.convert;
 
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

A custom ISO-week Converter in Spring

type conversion value object immutability

Intermediate 5 steps

rust

use axum::{
    async_trait,
    extract::{FromRequestParts, State},
    http::{header, request::Parts, StatusCode},

Custom auth extractors in Axum

extractors authentication error-handling

Intermediate 9 steps

ruby

class User < ApplicationRecord
  has_secure_password
 
  normalizes :email, with: ->(email) { email.strip.downcase }

Normalizing user input in Rails models

normalization validation data integrity

Intermediate 6 steps

python

import asyncio
import logging
from contextlib import asynccontextmanager
from datetime import datetime, timedelta, timezone

A background session cleaner in FastAPI

background-tasks asyncio lifespan

Intermediate 8 steps

javascript

function parseJwtPayload(token) {
  const parts = token.split('.');
  if (parts.length !== 3) {
    throw new Error('Invalid JWT: expected 3 segments');

Decoding a JWT payload in JavaScript

jwt base64url encoding

Intermediate 6 steps

go

package handlers
 
import (
	"errors"

Turning Gin binding errors into field messages

input validation struct tags error handling

Intermediate 9 steps

typescript

type EditorState = {
  content: string;
  cursor: number;
};

Undo/redo with two stacks in TypeScript

undo-redo stacks state-management

Intermediate 7 steps

java

import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.http.HttpClient;

Streaming a file download with Java's HttpClient

http-client streaming file-io

Intermediate 6 steps

ruby

class SemanticVersion
  include Comparable
 
  attr_reader :major, :minor, :patch, :prerelease

Comparable semantic versions in Ruby

comparable parsing operator-overloading

Intermediate 8 steps

php

<?php
 
namespace App\Jobs;

Serializing balance reconciliation in Laravel

queues concurrency idempotency

Intermediate 7 steps

python

import bisect
from typing import Sequence

Computing latency percentiles in Python

percentiles interpolation binary-search

Intermediate 8 steps

javascript

import { createContext, useContext, useReducer } from "react";
 
const WizardContext = createContext(null);

Building a form wizard with Context in React

context reducer state-management

Intermediate 10 steps

go

type Employee struct {
	Department string
	LastName   string
	FirstName  string

Multi-key sorting in Go

sorting comparators tie-breaking

Intermediate 6 steps

typescript

import { z, type ZodType } from "zod";
 
export class HttpError extends Error {
  constructor(

A type-safe fetch wrapper with Zod

generics runtime-validation error-handling

Intermediate 8 steps

java

@RestController
@RequestMapping("/api/documents")
@RequiredArgsConstructor
public class DocumentController {

Method-level authorization with @PreAuthorize in Spring

authorization spel rest-api

Intermediate 7 steps

rust

pub fn merge_intervals(mut intervals: Vec<(i64, i64)>) -> Vec<(i64, i64)> {
    if intervals.is_empty() {
        return Vec::new();
    }

Merging overlapping intervals in Rust

intervals sorting greedy

Intermediate 7 steps

php

<?php
 
namespace App\Services;

Phone verification codes in Laravel

rate-limiting caching hashing

Intermediate 7 steps

javascript

import { createContext, useContext, useReducer } from 'react';
 
const CartContext = createContext(null);

Building a shopping cart with Context in React

state management reducer context

Intermediate 10 steps