Intermediate code explainers

typescript

import {
  ArgumentsHost,
  Catch,
  ConflictException,

Turning TypeORM lock errors into 409s in NestJS

exception-handling optimistic-locking http-status

Intermediate 6 steps

python

from collections.abc import MutableMapping
 
 
class CaseInsensitiveDict(MutableMapping):

Building a case-insensitive dict in Python

data structures abstract base classes dunder methods

Intermediate 8 steps

java

public class TimedFetchService {
 
    private final ExecutorService executor = Executors.newFixedThreadPool(8);
    private final HttpClient httpClient = HttpClient.newHttpClient();

Enforcing HTTP timeouts with a Future

concurrency timeouts thread-pool

Intermediate 8 steps

php

<?php
 
namespace App\Http\Requests\DataObjects;

Typed request DTOs in Laravel

data-transfer-object validation immutability

Intermediate 6 steps

typescript

import { Component } from '@angular/core';
import { RouterLink, RouterLinkActive } from '@angular/router';
import { NgFor } from '@angular/common';

Building an active-route navbar in Angular

routing standalone-components accessibility

Intermediate 6 steps

go

package middleware
 
import (
	"net/http"

Role-based access control middleware in Gin

middleware authorization closures

Intermediate 7 steps

javascript

import { useCallback, useEffect, useState } from 'react';
 
export function useLocalStorage(key, initialValue) {
  const readValue = useCallback(() => {

How a useLocalStorage hook syncs state in React

custom hooks localstorage state persistence

Intermediate 8 steps

python

from fastapi import FastAPI, Request, status
from fastapi.encoders import jsonable_encoder
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse

Redacting sensitive fields in FastAPI errors

validation error-handling security

Intermediate 7 steps

java

@Component
public class RefreshTokenSuccessHandler implements AuthenticationSuccessHandler {
 
    private final RefreshTokenService refreshTokenService;

Issuing JWT and refresh tokens on login in Spring

authentication jwt http-cookies

Intermediate 7 steps

php

<?php
 
namespace App\Jobs;

Rendering invoice PDFs in a Laravel queue job

queued jobs pdf generation file storage

Intermediate 9 steps

typescript

type Masker = (value: string) => string;
 
const maskEmail: Masker = (value) => {
  const [local, domain] = value.split("@");

Recursively masking sensitive data for logs

recursion regex data-masking

Intermediate 9 steps

ruby

def render_table(rows)
  return "(no data)" if rows.empty?
 
  columns = rows.flat_map(&:keys).uniq

Rendering an ASCII table in Ruby

text-formatting column-alignment recursion

Intermediate 8 steps

javascript

import { useState } from 'react';
 
export function ReorderableList({ initialItems }) {
  const [items, setItems] = useState(initialItems);

Drag-to-reorder lists in React

drag-and-drop state-management immutable-updates

Intermediate 8 steps

python

from datetime import timedelta
 
from flask import Blueprint, current_app, make_response, redirect, request, url_for
from itsdangerous import URLSafeTimedSerializer, BadSignature, SignatureExpired

How signed remember-me cookies work in Flask

authentication signed-cookies session-management

Intermediate 8 steps

java

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.module.SimpleModule;

Serializing Money to JSON in Spring

serialization jackson money

Intermediate 8 steps

php

<?php
 
namespace App\Services;

Building a valid iCalendar feed in PHP in Laravel

ical serialization formatting

Intermediate 8 steps

ruby

class ApplicationController < ActionController::Base
  ALLOWED_REDIRECT_HOSTS = [nil, ENV.fetch("APP_HOST", "app.example.com")].freeze
 
  def store_return_to(location = request.fullpath)

Safe post-login redirects in Rails

open-redirect session authentication

Intermediate 9 steps

php

<?php
 
namespace App\View\Components;

Building a breadcrumb component in Laravel

blade components url parsing string manipulation

Intermediate 8 steps