Intermediate code explainers

java

public final class CaseConverter {
 
    private static final Pattern CAMEL_BOUNDARY =
            Pattern.compile("([a-z0-9])([A-Z])|([A-Z]+)([A-Z][a-z])");

Converting camelCase to snake_case in Java

regex string-manipulation utility-class

Intermediate 7 steps

ruby

class Membership < ApplicationRecord
  belongs_to :organization
  belongs_to :user

Enforcing scoped uniqueness in Rails

validations uniqueness callbacks

Intermediate 8 steps

typescript

import { Component, HostBinding, Input } from '@angular/core';
 
type ProgressVariant = 'success' | 'warning' | 'danger';

A CSS-driven progress ring in Angular

host-bindings css-custom-properties input-setters

Intermediate 8 steps

python

import heapq
from collections import Counter
from typing import Iterable, Hashable

Finding the top-N items in a stream

heaps counting generators

Intermediate 5 steps

php

<?php
 
namespace App\Providers;

Defining authorization gates in Laravel

authorization gates service-provider

Intermediate 6 steps

python

from flask import Blueprint, jsonify
from sqlalchemy import text
from sqlalchemy.exc import SQLAlchemyError

Building a health check endpoint in Flask

health-check blueprint error-handling

Intermediate 6 steps

java

@Component
public class RegionCacheWarmer implements SmartInitializingSingleton {
 
    private static final Logger log = LoggerFactory.getLogger(RegionCacheWarmer.class);

Warming a Spring cache at startup

caching startup-hook dependency-injection

Intermediate 7 steps

typescript

import { Controller, Param, Sse, MessageEvent } from '@nestjs/common';
import { Observable, interval, merge } from 'rxjs';
import { filter, map, takeWhile } from 'rxjs/operators';
import { JobService } from './job.service';

Streaming job progress with SSE in NestJS

server-sent-events reactive-streams rxjs

Intermediate 8 steps

go

package breaker
 
import (
	"errors"

How a circuit breaker works in Go

circuit-breaker state-machine concurrency

Intermediate 8 steps

php

<?php
 
final class TaskProgressReporter
{

Tracking task progress in a JSON file

state-persistence atomic-writes json

Intermediate 9 steps

rust

#[derive(Debug, Clone, PartialEq)]
pub enum Token {
    Number(f64),
    Plus,

How a tokenizer turns text into tokens

lexing enums iterators

Intermediate 8 steps

javascript

const MAX_FILE_SIZE = 5 * 1024 * 1024;
 
const ALLOWED_TYPES = {
  'image/jpeg': ['jpg', 'jpeg'],

Validating file uploads by content, not just claims

input-validation security magic-bytes

Intermediate 7 steps

python

import pandas as pd
import numpy as np

Cleaning a customer DataFrame with pandas

data-cleaning regex normalization

Intermediate 9 steps

java

public final class EmailNormalizer {
 
    private static final Pattern EMAIL_PATTERN = Pattern.compile(
        "^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}$"

Normalizing email addresses in Java

validation regex normalization

Intermediate 8 steps

typescript

import {
  Controller,
  All,
  Req,

Catch-all routes and error shaping in NestJS

exception-handling routing middleware

Intermediate 6 steps

javascript

function zip(keys, values) {
  if (keys.length !== values.length) {
    throw new RangeError('zip expects arrays of equal length');
  }

Three ways to zip arrays in JavaScript

arrays higher-order-functions pairing

Intermediate 6 steps

python

from datetime import date, timedelta
from typing import Annotated
 
from fastapi import APIRouter, Depends, Query

Validating date ranges with FastAPI dependencies

dependency-injection validation pydantic

Intermediate 6 steps

java

@RestController
@RequestMapping("/api/products")
@RequiredArgsConstructor
public class ProductBatchController {

Batch JSON Merge Patch in Spring

json-merge-patch rest-api partial-update

Intermediate 8 steps