Advanced code explainers

typescript

import { HttpService } from '@nestjs/axios';
import { Injectable, Logger, ServiceUnavailableException } from '@nestjs/common';
import { AxiosError } from 'axios';
import { catchError, firstValueFrom, retry, timer } from 'rxjs';

Resilient payment retries in NestJS

retry exponential-backoff rxjs

Advanced 8 steps

php

final class DebouncedSessionStore
{
    private array $pending = [];
    private array $timers = [];

Debouncing session writes with an event loop

debounce event-loop atomic-write

Advanced 9 steps

typescript

type Task<T> = () => Promise<T>;
 
export class Mutex {
  private queue: Array<() => void> = [];

Building an async mutex in TypeScript

concurrency promises locking

Advanced 7 steps

rust

use axum::{extract::State, http::StatusCode, response::IntoResponse, Json};
use chrono::{Duration, Utc};
use serde::{Deserialize, Serialize};
use std::{collections::HashMap, sync::Arc};

Refresh token rotation in Axum

authentication token-rotation reuse-detection

Advanced 9 steps

go

package middleware
 
import (
	"context"

How a request-timeout middleware works in Gin

middleware context goroutines

Advanced 6 steps

java

@Entity
@Table(name = "invoices")
@FilterDef(name = "tenantFilter", parameters = @ParamDef(name = "tenantId", type = String.class))
@Filter(name = "tenantFilter", condition = "tenant_id = :tenantId")

Multi-tenant row filtering with Hibernate in Spring

multi-tenancy hibernate filters request interceptor

Advanced 7 steps

rust

use axum::{
    extract::{FromRef, FromRequestParts},
    http::{request::Parts, StatusCode},
    response::{IntoResponse, Response},

A custom API-key extractor in Axum

authentication extractors trait-implementation

Advanced 8 steps

rust

use std::collections::HashSet;
use std::path::PathBuf;
use std::time::Duration;

Debouncing filesystem events in async Rust

debounce async channels

Advanced 7 steps

php

<?php
 
namespace App\Http\Controllers;

Streaming job progress with SSE in Laravel

server-sent-events streaming polling

Advanced 8 steps

rust

pub struct ScopeGuard<F: FnMut()> {
    rollback: F,
    active: bool,
}

A RAII rollback guard in Rust

raii error-handling closures

Advanced 8 steps

javascript

import { useCallback, useEffect, useRef } from 'react';
import { createPortal } from 'react-dom';
 
const FOCUSABLE = 'a[href], button:not([disabled]), textarea, input, select, [tabindex]:not([tabindex="-1"])';

Building an accessible modal in React

focus-trap accessibility portals

Advanced 9 steps

go

type SensorReading struct {
	DeviceID    string    `json:"device_id" binding:"required"`
	Temperature float64   `json:"temperature"`
	RecordedAt  time.Time `json:"recorded_at" binding:"required"`

Streaming NDJSON ingestion in Gin

streaming batching json-decoding

Advanced 10 steps

python

from decimal import Decimal
 
from django.db import transaction
from django.core.exceptions import ValidationError

Placing an order atomically in Django

transactions row-locking concurrency

Advanced 9 steps

go

package fetcher
 
import (
	"context"

Bounded-concurrency HTTP fetching in Go

concurrency semaphore context-cancellation

Advanced 9 steps

php

<?php
 
namespace App\Services;

Placing an order atomically in Laravel

transactions pessimistic-locking concurrency

Advanced 8 steps

typescript

type JsonValue = Record<string, unknown> | unknown[];
 
export function parseJsonStream<T = JsonValue>(
  stream: ReadableStream<Uint8Array>,

Streaming JSON parsing with a depth counter

streams parsing state-machine

Advanced 9 steps

java

@Aspect
@Component
public class IdempotencyAspect {

How an idempotency aspect works in Spring

aop idempotency caching

Advanced 9 steps

typescript

import { useEffect, useRef, useCallback } from "react";
 
type DraftPayload = Record<string, unknown>;

A debounced auto-save hook in React

debouncing request-cancellation refs

Advanced 7 steps