Intermediate code explainers

python

from flask import Blueprint, render_template, request, abort
from sqlalchemy import select
 
from .models import Article

Paginating articles in a Flask Blueprint

pagination blueprints input-validation

Intermediate 6 steps

javascript

import { notFound } from 'next/navigation';
 
const PER_PAGE = 24;
const SORT_OPTIONS = ['relevance', 'price-asc', 'price-desc', 'newest'];

Parsing search params in a Next.js page

input-validation query-params pagination

Intermediate 10 steps

go

package collection
 
func Deduplicate[T comparable](items []T) []T {
	seen := make(map[T]struct{}, len(items))

Generic deduplication in Go

generics deduplication maps

Intermediate 5 steps

ruby

require 'optparse'
require 'ostruct'
 
def parse_options(argv)

Parsing CLI options with OptionParser

cli argument-parsing validation

Intermediate 8 steps

rust

use axum::{extract::Form, http::StatusCode, response::{IntoResponse, Response}, Json};
use serde::Deserialize;
use serde_json::json;
use std::collections::HashMap;

Validating a signup form in Axum

form-validation deserialization error-handling

Intermediate 8 steps

java

package com.example.monitoring;
 
import org.springframework.boot.actuate.health.Health;
import org.springframework.boot.actuate.health.HealthIndicator;

A custom replica health check in Spring

health-check actuator monitoring

Intermediate 7 steps

javascript

import { NextResponse } from 'next/server';
import Stripe from 'stripe';
import { headers } from 'next/headers';

Handling Stripe webhooks in Next.js

webhooks signature verification payment processing

Intermediate 7 steps

go

func StreamMetrics(c *gin.Context) {
	clientGone := c.Request.Context().Done()
	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()

Streaming server-sent events in Gin

server-sent-events streaming channels

Intermediate 7 steps

python

from fastapi import APIRouter, Depends, Query
from pydantic import BaseModel
from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

How a paginated list endpoint works in FastAPI

pagination dependency-injection async-orm

Intermediate 8 steps

ruby

module Retryable
  class RetriesExhausted < StandardError; end
 
  RETRYABLE_ERRORS = [

Exponential backoff retries in Ruby

retry-logic exponential-backoff error-handling

Intermediate 7 steps

typescript

import { IsEmail, IsEnum, IsInt, IsOptional, IsString, Length, Max, Min } from 'class-validator';
import { Type } from 'class-transformer';
import { Body, Controller, Post } from '@nestjs/common';

How DTO validation works in NestJS

validation data-transfer-objects decorators

Intermediate 8 steps

go

package worker
 
import (
	"fmt"

A graceful worker pool in Go

concurrency goroutines channels

Intermediate 7 steps

javascript

async function pollJobUntilComplete(jobId, { interval = 2000, timeout = 60000, signal } = {}) {
  const deadline = Date.now() + timeout;
 
  while (true) {

Polling a job until it finishes in JavaScript

polling async-await abortsignal

Intermediate 6 steps

ruby

class Throttle
  def initialize(interval)
    @interval = interval
    @mutex = Mutex.new

A thread-safe throttle in Ruby

concurrency rate-limiting mutex

Intermediate 7 steps

typescript

type CheckoutState = "cart" | "shipping" | "payment" | "review" | "confirmed";
 
type CheckoutEvent =
  | { type: "PROCEED" }

A typed checkout state machine in TypeScript

state-machine union-types type-safety

Intermediate 7 steps

rust

use axum::{
    body::Body,
    extract::Path,
    http::{header, StatusCode},

Streaming file downloads in Axum

streaming file-serving path-traversal

Intermediate 8 steps

java

import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;

Three ways to deduplicate a list by key in Java

streams deduplication collectors

Intermediate 6 steps

php

<?php
 
function verifyJwt(string $token, string $secret): array
{

Verifying an HS256 JWT in PHP

jwt hmac authentication

Intermediate 9 steps