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Python Redis: Caching and Fast Data Structures Redis is an in-memory data store used for caching, session storage, pub/sub messaging, leaderboards, rate limiting, and more. With redis-py 's async client, it integrates cleanly into any asyncio application. Installation pip install redis[hiredis] # hiredis is a C parser — 2-5× faster protocol parsing Connect and Verify import asyncio import redis.asyncio as aioredis from datetime import timedelta import json REDIS_URL = " redis://localhost:6379/0 " async def get_redis () -> aioredis . Redis : client = aioredis . from_url ( REDIS_URL , encoding = " utf-8 " , decode_responses = True , socket_connect_timeout = 5 , socket_timeout = 5 , retry_on_timeout = True , ) pong = await client . ping () print ( f " Redis connected: { pong } " ) return client Strings — Basic Cache with TTL async def cache_set ( r : aioredis . Redis , key : str , value : str , ttl : int = 300 ) -> None : await r . set ( key , value , ex = ttl ) async def cache_get ( r : aioredis . Redis , key : str ) -> str | None : return await r . get ( key ) # Cache-aside pattern async def get_user_profile ( r : aioredis . Redis , user_id : int , db ) -> dict : cache_key = f " user:profile: { user_id } " cached = await r . get ( cache_key ) if cached : print ( f " Cache HIT for user { user_id } " ) return json . loads ( cached ) print ( f " Cache MISS for user { user_id } — querying DB " ) user = await db . fetch_user ( user_id ) # your DB call if user : await r . set ( cache_key , json . dumps ( user ), ex = 600 ) return user or {} # Atomic counter async def increment_page_views ( r : aioredis . Redis , page : str ) -> int : key = f " views: { page } " count = await r . incr ( key ) await r . expire ( key , 86400 ) # reset counter after 24 h return count Hashes — Structured Objects async def save_session ( r : aioredis . Redis , session_id : str , data : dict , ttl : int = 3600 ) -> None : key = f " session: { session_id } " await r . hset ( key , mapping = data )

In the previous article , we briefly discussed the relationship between Cookies and CORS . In this article, we'll take a closer look at how browsers decide whether a Cookie should be included in a Cross-Origin request. One of the most common misconceptions is that once CORS is configured correctly, Cookies are automatically sent with every request. In reality, that's not how browsers work. 📌 Default Browser Behavior When a Cross-Origin request is made using fetch() or XMLHttpRequest , browsers do not send Cookies, Authorization headers, or other credentials by default. For example: fetch ( " https://api.example.com/profile " ) Even if the user is already logged into api.example.com , the browser will not include any Cookies with this request. This default behavior helps prevent authentication data from being unintentionally leaked across different Origins. 📌 How Can We Send Cookies? If you want the browser to include Cookies in a Cross-Origin request, you must explicitly use the credentials option. For example: fetch ( " https://api.example.com/profile " , { credentials : " include " }) Using credentials: "include" does not guarantee that Cookies will be sent. Instead, it tells the browser: "If there are any Cookies that are eligible to be sent with this request, include them." 📌 What Makes a Cookie Eligible? Even with credentials: "include" , the browser still evaluates the Cookie before sending it. Some of the most important checks include: Domain Path SameSite For example: If the Cookie's Domain doesn't match the request destination, it won't be sent. If the request path doesn't satisfy the Cookie's Path attribute, it won't be sent. If the Cookie's SameSite policy blocks Cross-Site requests, it won't be sent. In other words, credentials is only the first requirement , not the final decision. 📌 Server Configuration Matters Too If your application expects JavaScript to access the response while using Cookies, the server must also be configured correctly. For exampl

You've written setTimeout(fn, 0) expecting it to run "immediately." It didn't. A Promise.then() you scheduled a line later ran first, and somewhere a for loop of 50,000 iterations froze your UI for a full second despite every function being "async." None of this is a bug. It's the JavaScript event loop doing exactly what it always does — you just haven't seen the mechanism yet. What you'll learn By the end of this guide you'll be able to: Explain, precisely, why microtasks (Promises) always run before macrotasks ( setTimeout , setInterval ) — even at a zero delay Predict the exact console output order of any mix of synchronous code, setTimeout , and await Diagnose a frozen UI as a blocked call stack, not a "slow async function" Choose correctly between queueMicrotask , setTimeout(fn, 0) , and requestAnimationFrame for a given timing need Avoid the two most common event-loop bugs: microtask starvation and accidental serial await s in a loop Who this is for: you've written async / await and used setTimeout , but you want the model that makes their interaction predictable instead of memorized. Contents Why the JavaScript event loop exists The mental model Stage 1: the call stack and blocking code Stage 2: Web APIs and the macrotask queue Stage 3: Promises and the microtask queue Stage 4: async/await is sugar, not magic Stage 5: rendering, and Node's extra queues Edge cases and gotchas Best practices FAQ Cheat sheet Key takeaways Why the JavaScript event loop exists JavaScript runs on a single thread. One call stack, one thing executing at a time, no parallel function calls in the same realm. That's a deliberate design — it means you never need locks or mutexes to protect a shared variable — but it creates an obvious problem: how does a single-threaded language do anything concurrent, like waiting on a network response, without freezing the entire page while it waits? Here's the naive expectation, and why it would be a disaster if JavaScript worked this way: console . l

Videos are one of the heaviest assets you can add to a web page. Loading videos too early can significantly impact your application's performance. The good news is that modern browsers are starting to support lazy loading for video elements , allowing you to defer loading until users are likely to watch them. However, there's one important thing to know: 👉 This feature is not yet part of the Baseline web platform , so browser support is still limited. At the time of writing, lazy loading for <video> elements is supported in Chromium-based browsers such as Google Chrome , Microsoft Edge , and Opera , while browsers like Firefox and Safari do not yet support it natively. In this article, we'll explore: What lazy loading videos is Why it's important for web performance How to implement it Browser support considerations Best practices for optimizing video loading Let's dive in. 🤔 What Is Lazy Loading for Videos? Lazy loading means delaying the loading of a resource until it's actually needed. Instead of downloading every video immediately during page load, the browser waits until the video is close to entering the viewport. This helps reduce: initial network requests bandwidth usage page load time memory consumption Especially on pages with multiple videos, the difference can be significant. 🟢 What Problem Does It Solve? Imagine an e-commerce page with several product videos. Without lazy loading: every video starts downloading immediately bandwidth is consumed even for videos users never watch page rendering may become slower This negatively impacts; Largest Contentful Paint (LCP), Time to Interactive (TTI), and overall user experience. Most visitors won't watch every video on the page. So why load them all? Lazy loading ensures videos are fetched only when they're actually needed. 🟢 How to Lazy Load a Video The easiest approach is using the loading="lazy" attribute. Example: <video controls loading= "lazy" poster= "/preview.jpg" > <source src= "/video.mp4" type= "vide

I Tested Direct Provider APIs vs Aggregators — Here's the Truth Six months ago I was staring at a $48,000 invoice from an AI provider that shall not be named. We had committed to a six-month contract because the sales rep promised "priority routing" and "negotiated rates." What we got instead was a rate hike, an outage during our biggest product launch, and a support team that took 72 hours to respond. That was the moment I decided to stop signing contracts with AI providers entirely. This is the playbook I wish someone had handed me on day one — the architecture decisions, the math, and the code that lets a small team punch way above its weight class without betting the company on a single vendor. The Trap Most Startups Fall Into When I started my last company, I did what every founder does. I read the docs, got an API key, shipped a feature. The model worked, the demo went well, the investors nodded. Then we hit production traffic and the bills started arriving like clockwork. Here's what nobody tells you about going direct to a model provider as a startup: The pricing page you see on the website is the retail price. The actual cost of running production workloads includes rate limits you didn't anticipate, caching you forgot to implement, context windows that blow up your token count, and prompt engineering iterations that look cheap per call but compound fast. I watched one team burn $20K in a single weekend because they were streaming completions without setting a max_tokens guardrail. Direct providers also lock you into their ecosystem. Their SDK, their tools, their prompt format, their authentication scheme. The moment you want to A/B test a different model — which you will, probably next quarter — you're rewriting integration code instead of shipping features. And then there's the geopolitical mess. Some of the best models in 2026 come from providers that don't accept US credit cards. I've personally lost an afternoon trying to sign up for an account that re

Introdução Validar dados é uma responsabilidade que pode ficar na aplicação, no banco de dados, ou em ambos. Deixar tudo na aplicação é arriscado: diferentes sistemas podem acessar o mesmo banco, migrações podem rodar diretamente, um bug pode deixar passar um valor inválido. Constraints são regras definidas no próprio banco de dados — uma camada de proteção que age independente de quem está escrevendo os dados. PRIMARY KEY A chave primária identifica cada linha de forma única. Ela combina duas restrições implicitamente: NOT NULL e UNIQUE . Nenhuma linha pode ter o mesmo valor de chave primária, e nenhuma pode tê-la nula. CREATE TABLE clientes ( id INT PRIMARY KEY , nome VARCHAR ( 100 ) NOT NULL ); Quando a chave primária envolve mais de uma coluna, ela é declarada separadamente: CREATE TABLE matriculas ( aluno_id INT , curso_id INT , PRIMARY KEY ( aluno_id , curso_id ) ); Na maioria dos bancos, é comum usar uma chave primária auto-incremental para não precisar gerenciar os IDs manualmente: -- PostgreSQL id SERIAL PRIMARY KEY -- MySQL id INT AUTO_INCREMENTPRIMARY KEY -- SQL padrão (suportado por ambos) id INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY FOREIGN KEY A chave estrangeira garante integridade referencial : um valor só pode existir numa coluna se ele existir como chave primária na tabela referenciada. É o que torna os relacionamentos entre tabelas confiáveis. CREATE TABLE pedidos ( id INT PRIMARY KEY , cliente_idINT REFERENCES clientes ( id ) ); Tentar inserir um pedido com cliente_id = 99 quando não existe cliente com esse id resulta em erro imediato. O banco rejeita a operação antes mesmo de ela chegar ao disco. O comportamento quando o registro referenciado é deletado pode ser configurado: CREATE TABLE pedidos ( id INT PRIMARY KEY , cliente_id INT REFERENCES clientes ( id ) ON DELETE CASCADE -- deleta os pedidos junto com o cliente ON UPDATE CASCADE -- atualiza o cliente_id se o id do cliente mudar ); As opções disponíveis são: Opção Comportamento RESTRICT

Introdução Consultas individuais respondem perguntas como "qual o email do cliente 42?". Mas as perguntas mais valiosas em qualquer sistema são de outro tipo: "qual o produto mais vendido?", "qual a receita média por pedido?", "quantos clientes se cadastraram esse mês?". Para responder isso, o SQL oferece as funções de agregação — operações que recebem um conjunto de linhas e devolvem um único valor resumido. Para os exemplos a seguir, considere esta tabela: pedidos: | id | cliente | produto | categoria | quantidade | valor | |----|------------|-------------|--------------|------------|--------| | 1 | Ana Lima | Notebook | Eletrônicos | 1 | 3500.00| | 2 | Ana Lima | Mouse | Periféricos | 2 | 80.00| | 3 | Bruno Melo | Teclado | Periféricos | 1 | 150.00| | 4 | Bruno Melo | Notebook | Eletrônicos | 1 | 3500.00| | 5 | Carla Nunes| Monitor | Eletrônicos | 2 | 1200.00| | 6 | Carla Nunes| Mouse | Periféricos | 1 | 80.00| As Funções de Agregação COUNT Conta o número de linhas — ou de valores não nulos em uma coluna específica. -- Total de pedidos SELECT COUNT ( * ) AS total_pedidosFROM pedidos ; -- Resultado: 6 -- Clientes distintos que fizeram pedidos SELECT COUNT ( DISTINCT cliente ) AS clientes_unicosFROM pedidos ; -- Resultado: 3 COUNT(*) conta todas as linhas, incluindo as que têm nulos. COUNT(coluna) conta apenas as linhas onde aquela coluna não é nula. COUNT(DISTINCT coluna) conta valores únicos — útil para saber quantos clientes, produtos ou categorias distintos aparecem no resultado. SUM Soma os valores de uma coluna numérica. -- Receita total SELECT SUM ( valor ) AS receita_total FROM pedidos ; -- Resultado: 8510.00 -- Total de itens vendidos SELECT SUM ( quantidade ) AS itens_vendidos FROM pedidos ; -- Resultado: 8 AVG Calcula a média aritmética dos valores. -- Valor médio por pedido SELECT AVG ( valor ) AS ticket_medio FROM pedidos ; -- Resultado: 1418.33 AVG ignora valores nulos automaticamente — calcula a média apenas sobre os registros que têm valor preenchid

If you need real-time BTC conversion (USD and BRL), polling an API every few seconds is usually not enough. A better approach is streaming quotes with WebSockets and calculating conversions as events arrive. Why WebSockets for BTC conversion? With WebSockets, your app keeps one open connection and receives new prices instantly. Benefits: Lower latency than polling Fewer HTTP requests Better user experience for real-time values Trade-offs: You must handle reconnects Need heartbeat/health checks Must validate and normalize incoming messages Real-time conversion model For BTC conversion, a common model is: Stream BTC/USD Stream USD/BRL Calculate BTC/BRL = BTC/USD × USD/BRL This avoids waiting for a separate BTC/BRL endpoint and keeps conversion logic transparent What is a “tick”? A tick is one market update event. Example: BTCUSD changed to 64210.50 at timestamp t . In this article, each tick has: pair : market identifier ( BTCUSD , USDBRL ) price : latest value for that pair ts : event timestamp Why this matters: conversion state should always be derived from the latest ticks . Minimal WebSocket client (TypeScript) This client only transports responsibilities: Connect Receive messages Parse and normalize into a consistent shape Notify listeners Reconnect on disconnect type MarketTick = { pair : string ; // e.g. "BTCUSD" or "USDBRL" price : number ; ts : number ; }; class WsFeedClient { private ws ?: WebSocket ; private listeners : Array < ( tick : MarketTick ) => void > = []; constructor ( private readonly url : string ) {} connect () { this . ws = new WebSocket ( this . url ); this . ws . onopen = () => console . log ( " [ws] connected " ); this . ws . onmessage = ( event ) => { try { const data = JSON . parse ( String ( event . data )); // Normalize external payload into internal contract const tick : MarketTick = { pair : String ( data . pair ), price : Number ( data . price ), ts : Number ( data . ts ), }; // Basic guard if ( ! tick . pair || Number . isNaN ( tick

"AI agent" gets thrown around so much I figured I should just build one instead of reading more threads about it. The core idea turned out to be small: you put Claude in a loop and hand it some tools. It picks a tool, you run it, you hand back the result, and it keeps going until it has an answer. Code is here if you want to skip ahead: claude-research-agent . What it can do Give it a task and it works out the steps on its own. Mine can: search the web (no API key for this part, it just hits DuckDuckGo's HTML page) open a URL and pull the readable text out do math without me trusting eval run read-only SQL against a SQLite file read local files, but only inside the project folder save findings to a notes file The loop is basically the whole thing Honestly this is most of it: messages = [{ " role " : " user " , " content " : user_message }] for _ in range ( MAX_STEPS ): response = client . messages . create ( model = " claude-sonnet-5 " , max_tokens = 2048 , tools = TOOL_SCHEMAS , messages = messages , ) messages . append ({ " role " : " assistant " , " content " : response . content }) if response . stop_reason != " tool_use " : return final_text ( response ) tool_results = [] for block in response . content : if block . type == " tool_use " : result = run_tool ( block . name , block . input ) tool_results . append ({ " type " : " tool_result " , " tool_use_id " : block . id , " content " : result , }) messages . append ({ " role " : " user " , " content " : tool_results }) The thing to watch is stop_reason . If Claude says tool_use , it wants you to run something. You run it, drop the result back into the conversation as a tool_result , and loop. When it stops asking for tools, you're done. The MAX_STEPS cap is just there so a confused agent can't spin forever. Tools are just functions Each tool is a Python function plus a little JSON schema telling Claude when to reach for it. Want a new capability? Write a function, add its schema. The loop never changes, which w

Kiponos Java SDK 5.0 What’s New — Developer Guide This is the technical companion to the 5.0 milestone announcement: what changed, how modes behave, how to read config with the Folder API, and how to upgrade cleanly. Version 5.0.0.260710 Maven group io.kiponos Artifacts sdk-boot-3 (recommended), sdk-boot-2 (legacy) Released 2026-07-12 (Maven Central) Happy product story: SDK 5.0 milestone post . 1. Summary for busy engineers 5.0 productizes client reliability using a classic state pattern behind a stable facade: Mode When Config reads Mutations / hooks Notes Ready Connected to hub Live in-memory tree Full Production happy path Offline Disconnected but LKG available Last Known Good (read-only) No-op / ignored Survives hub blips without inventing values Safe Fail-closed Empty / null-safe No-op Diagnostic dumps must not overwrite LKG Public entry remains: Kiponos kiponos = Kiponos . createForCurrentTeam (); You do not receive mode instances as the API surface. Modes switch internally. Query with: kiponos . getCurrentMode (); kiponos . isReadyMode (); kiponos . isOfflineMode (); kiponos . isSafeMode (); 2. Install Gradle — Boot 3 repositories { mavenCentral () } dependencies { implementation 'io.kiponos:sdk-boot-3:5.0.0.260710' } Gradle — Boot 2 implementation 'io.kiponos:sdk-boot-2:5.0.0.260710' Runtime inputs Input Mechanism Identity env KIPONOS_ID Access env KIPONOS_ACCESS Profile / tree slice JVM -Dkiponos="['App']['1.0.0']['dev']['base']" Tokens and profile come from the Kiponos Connect screen for your team. sdk-common is not a separate app dependency for consumers — boot jars include shared classes (fat-jar pattern). 3. Architecture (state pattern) Application code │ ▼ Kiponos / KiponosBase ◄── stable facade (one reference for app lifetime) │ ▼ volatile SdkState ├── ReadyMode* → live WebSocket + full Folder ops ├── OfflineMode* → LKG reads only └── SafeMode* → fail-closed + safe diagnostic dump Design rule: never return Ready/Offline/Safe objects to callers. Retur

The Developer's Guide to Picking the Right Coding LLM at Scale Six months ago, I was staring at our monthly AI bill — $14,000 and climbing fast. We were using the "premium" model for everything, including trivial code completions. That night, I built a small internal benchmark to figure out which models actually earn their cost. What I learned reshaped how we think about AI tooling, vendor lock-in, and what "production-ready" really means. Here's the raw truth from my testing rig, what we shipped, and how we cut costs by 70% without touching output quality. Why I Stopped Trusting Default Recommendations Every vendor says their model is the best. Every benchmark site ranks things differently. Most "best of" lists are either sponsored or built on vibes. I needed numbers that matched my actual workflow: generating Python services, debugging JavaScript race conditions, implementing TypeScript algorithms, and reviewing Go for security. So I took ten models, threw identical prompts at them, and scored them myself. No vendor PR. No cherry-picked examples. Just the same five tasks, run the same way, scored on the same rubric. Here are the ten models I tested, with their output pricing per million tokens — because at scale, that's the metric that decides whether your AI strategy is viable or a margin killer. Model Provider Output $/M DeepSeek V4 Flash DeepSeek $0.25 DeepSeek Coder DeepSeek $0.25 Qwen3-Coder-30B Qwen $0.35 DeepSeek V4 Pro DeepSeek $0.78 DeepSeek-R1 DeepSeek $2.50 Kimi K2.5 Moonshot $3.00 GLM-5 Zhipu $1.92 Qwen3-32B Qwen $0.28 Hunyuan-Turbo Tencent $0.57 Ga-Standard GA Routing $0.20 Before you ask: yes, I tested against the originals. I also tested against Global API's unified routing layer, which lets you hit any of these through one endpoint. More on that later — it became the architectural decision that actually saved us. My Benchmark Methodology (No Marketing Fluff) I built five tasks that mirror what my engineers actually do every week. Not synthetic acad

If you’ve ever struggled with CALCULATE() or wondered why SUMX() behaves differently from SUM() , this guide is for you. DAX (Data Analysis Expressions) is the language that powers Power BI , Analysis Services , and Power Pivot — enabling dynamic calculations, filtering, and time intelligence. Below is a categorized cheat sheet of essential DAX functions , plus examples showing how to use each in real-world Power BI scenarios. Filtering & Context These functions control how filters are applied and evaluated in your calculations. Function Example Description CALCULATE() CALCULATE(SUM(Sales[Amount]), Region[Name] = "Nairobi") Changes filter context to calculate total sales for Nairobi. FILTER() FILTER(Sales, Sales[Amount] > 10000) Returns a table filtered by condition. ALL() CALCULATE(SUM(Sales[Amount]), ALL(Region)) Ignores filters on Region. REMOVEFILTERS() CALCULATE(SUM(Sales[Amount]), REMOVEFILTERS(Region)) Removes filters from Region. VALUES() VALUES(Customer[City]) Returns unique list of cities. SELECTEDVALUE() SELECTEDVALUE(Product[Category], "All") Returns selected category or “All” if none. TREATAS() TREATAS(VALUES(Temp[City]), Customer[City]) Applies one table’s values as filters on another. KEEPFILTERS() CALCULATE(SUM(Sales[Amount]), KEEPFILTERS(Product[Category] = "Electronics")) Keeps existing filters and adds new ones. ALLSELECTED() CALCULATE(SUM(Sales[Amount]), ALLSELECTED(Region)) Respects user selections in visuals. ALLEXCEPT() CALCULATE(SUM(Sales[Amount]), ALLEXCEPT(Sales, Sales[Year])) Removes all filters except Year. Aggregation Summarize or aggregate data across rows or columns. Function Example Description SUM() SUM(Sales[Amount]) Adds all sales amounts. AVERAGE() AVERAGE(Sales[Amount]) Calculates mean value. COUNT() COUNT(Customer[ID]) Counts non-blank entries. COUNTROWS() COUNTROWS(Sales) Counts rows in a table. DISTINCTCOUNT() DISTINCTCOUNT(Customer[ID]) Counts unique customers. MIN() MIN(Sales[Amount]) Finds smallest sale. MAX() MAX(Sales[Amo

I built a small index basket app on Robinhood Chain because I wanted to understand the developer path from the first contract deploy all the way to a working frontend. The app is intentionally plain: a user deposits Stock Tokens, which are blockchain tokens that represent real equity exposure, and receives an ERC-20 basket share. ERC-20 is Ethereum's standard token interface, so a compatible token exposes familiar methods like balanceOf , transfer , and approve . The basket share is priced from live price feeds, and the user can redeem it back into the underlying Stock Tokens. That's the part that made this interesting to me. The chain is custom, but the app path is not. I still wrote Solidity, deployed with Foundry, read contract state with viem, and wrote transactions from React with wagmi. If you've built normal web apps, think of the chain's RPC endpoint as the API base URL. A wallet is login plus a signing key. A smart contract is backend code you deploy to the chain, except you should treat it like immutable infrastructure because you don't get to hot-patch it casually later. The demo and source are here: App: https://robinhood-chain-dapp.vercel.app/ Code: https://github.com/hummusonrails/robinhood-chain-dapp-example The custom chain still feels like the EVM Robinhood Chain is a custom Arbitrum Chain, which means it runs as a dedicated chain on the stack of Arbitrum, an Ethereum scaling system. It is also EVM-compatible. EVM means Ethereum Virtual Machine, the runtime that executes Solidity contracts, so the tooling surface looks like the Ethereum developer flow many tutorials already teach. An L2, or rollup, is a chain that executes transactions separately and then posts compressed proof or transaction data back to Ethereum. Robinhood Chain uses Ethereum blobs for data availability, which is a cheaper Ethereum data lane for rollups to publish the data needed to reconstruct chain state. Gas, the metered compute fee you pay to run transactions, is paid in ETH.

You've got a JSON API response and you want TypeScript interfaces for it. Here's how to generate them fast — and where the auto-generators quietly get it wrong. The fast path Paste your JSON, get interfaces: { "id" : 1 , "name" : "Ada" , "roles" : [ "admin" ], "profile" : { "active" : true } } → interface Root { id : number ; name : string ; roles : string []; profile : Profile ; } interface Profile { active : boolean ; } jsonviewertool.com/json-to-typescript does this in the browser (client-side), nesting objects into their own interfaces. Where generators trip up A generator only sees the ONE sample you give it, which causes predictable gaps: Nullable fields. If your sample has "avatar": null , the generator infers null — but the real type is probably string | null . Feed it a populated sample, or fix it by hand. Empty arrays. "tags": [] infers any[] — the element type is unknowable from an empty array. Optional fields. A field missing from your sample won't appear at all. If the API sometimes omits middleName , mark it middleName?: string . Unions. A status that's "active" in your sample becomes string , not the literal union "active" | "banned" | "pending" . Narrow it manually for the safety. Numbers that are really enums or IDs. "currency": 840 types as number ; you may want an enum or branded type. When to use a schema instead If the JSON has a JSON Schema or OpenAPI spec, generate types from that ( json-schema-to-typescript , openapi-typescript ) — it encodes nullability, optionality, and unions the raw sample can't. Sample-based generation is for quick throwaway typing; schema-based is for anything you'll maintain. Rule of thumb Generate from a sample to skip the boilerplate, then read every field — the generator gives you a draft, not a contract. Nullability and optional fields are where the runtime bugs hide.

I've been building apps with IndexedDB for years. The local part works fine — store data, query it, show it on screen. The hard part is keeping that data in sync with a server when the network comes and goes. Most tutorials show you how to build an offline app with a framework. Firebase, RxDB, WatermelonDB. Those work, but they bring their own abstractions, their own sync protocols, their own opinions. I wanted something simpler. A database with a sync API that doesn't dictate how my backend works. Here's the setup I landed on. npm: npm install ctrodb Docs: ctrodb.vercel.app/docs/sync/overview What We're Building A notes app that works offline. Create and edit notes on the train, in a tunnel, on a plane. When the network comes back, everything syncs automatically. The database is ctrodb (zero-dependency, browser-based). The backend is anything that speaks HTTP. Step 1: Database Setup import { Database , syncPlugin , HttpTransport } from " ctrodb " const db = new Database ({ name : " notes-app " , schema : { version : 1 , collections : { notes : { fields : { title : { type : " string " , required : true }, body : { type : " string " }, updatedAt : { type : " string " , default : () => new Date (). toISOString () }, }, indexes : [{ field : " updatedAt " }], }, }, }, }) await db . connect () Every collection you want to sync needs a timestamp field. The sync engine uses it to order changes and detect conflicts. Plugins are passed in the Database constructor via plugins array: const transport = new HttpTransport ({ url : " https://api.myapp.com/sync " , }) const db = new Database ({ name : " notes-app " , schema : { ... }, plugins : [ syncPlugin ({ transport })], }) await db . connect () The transport takes a single base URL and appends /push and /pull automatically. The sync plugin hooks into every write operation and records it in the change log. The plugin exposes devtools that take the database instance as their first argument: import { inspectSyncQueue , retryFaile

Conditional Statements Conditional statements allow JavaScript to execute different blocks of code based on whether a condition is true or false. if - The if statement executes a block of code only if the condition is true. if...else - Use if...else when you want one block of code to run if the condition is true and another block if it's false. if...else if...else - Use this when you have multiple conditions to check. switch statement - The switch statement is used when you have many possible values for one variable. Nested if statement - You can also write an if statement inside another if. Ternary Operator - An optimized one-line shorthand for standard if...else blocks ** If Statement ** let age = 20 ; if ( age >= 18 ) { console . log ( " Eligible to vote " ); } //Output: Eligible to vote ** if else Statement ** let age = 16 ; if ( age >= 18 ) { console . log ( " Eligible to vote " ); } else { console . log ( " Not eligible to vote " ); } // Output: Not eligible to vote ** if ... else if ... else ** let marks = 85 ; if ( marks >= 90 ) { console . log ( " Grade A " ); } else if ( marks >= 75 ) { console . log ( " Grade B " ); } else if ( marks >= 50 ) { console . log ( " Grade C " ); } else { console . log ( " Fail " ); } // Output: Grade B ** switch statement ** let day = 3 ; switch ( day ) { case 1 : console . log ( " Monday " ); break ; case 2 : console . log ( " Tuesday " ); break ; case 3 : console . log ( " Wednesday " ); break ; default : console . log ( " Invalid Day " ); } // Output: Wednesday // Important: The break statement stops the execution after the matching case.We must compulsory to use break statement because if you don't use break, JavaScript will continue executing the next cases even the output is correct. ** Nested if Statement ** let age = 20 ; let hasLicense = true ; if ( age >= 18 ) { if ( hasLicense ) { console . log ( " You can drive. " ); } } // Output: You can drive. ** Ternary Operator ** let isLoggedIn = true ; let systemMessage = is

Have you ever wondered how massive modern platforms like Netflix, PayPal, and LinkedIn handle millions of users simultaneously without crashing? The secret weapon behind much of the modern web is Node.js. Traditionally, JavaScript—the language that makes websites interactive—could only run inside a web browser like Chrome or Edge. Node.js changed the game by freeing JavaScript from the browser, allowing it to run directly on your computer. This means you can use it to build backend servers, automate boring computer tasks, or run powerful development tools. If you are intimidated by coding, don't worry. This guide will take you from zero to running your very first Node.js program on Windows, step-by-step. Prerequisites Before we begin, you only need two things: A computer running Windows 10 or 11. An active internet connection to download the installer. No prior coding experience or command-line knowledge is required! Step-by-Step Instructions Download the Node.js Installer First, we need to grab the official installation file. Open your web browser and go to the official website: nodejs.org. You will see two primary options to download. Always choose the LTS (Long Term Support) version. The LTS version is heavily tested, stable, and less likely to give you unexpected errors. Click the Windows Installer button to download the .msi file to your computer. Run the Setup Wizard Once the download finishes, navigate to your Downloads folder and double-click the file to open the setup wizard. Click Next on the welcome screen. Accept the license agreement and click Next. Leave the default installation folder as it is (C:\Program Files\nodejs) and click Next. On the "Custom Setup" screen, leave everything at its default and click Next. Important Step: You will see a checkbox that asks to "Automatically install the necessary tools." Leave this unchecked for now to keep your setup simple and fast. Click Next. Finally, click Install. If Windows asks for permission to make change

A container's writable layer feels like a filesystem, and that's exactly the trap. Write a database into it, remove the container, and the data is gone — no warning, no recovery. If you want anything to survive docker rm , it has to live outside the container, and Docker gives you three ways to do that: named volumes, bind mounts, and tmpfs. Knowing which one to reach for is most of the battle. Why the writable layer betrays you Every running container gets a thin read-write layer stacked on top of its image layers. It looks persistent because you can docker exec in and see your files. But that layer is bound to the container's lifecycle. docker run --name scratch alpine sh -c 'echo hello > /data.txt; cat /data.txt' # hello docker rm scratch # the layer — and /data.txt — no longer exists There's no "oops." The writable layer is discarded with the container. Persistence is not a default you get; it's a decision you make. That decision is a volume, a bind mount, or tmpfs. Named volumes: the default for state A named volume is storage that Docker creates and manages for you. You give it a name, Docker keeps the actual bytes under its own directory, and you never have to care where that is. docker volume create pgdata docker run -d --name db \ --mount type = volume,source = pgdata,target = /var/lib/postgresql/data \ postgres:16 The container writes to /var/lib/postgresql/data , but those bytes land in a Docker-managed location on the host. Remove and recreate the container against the same volume and the data is still there. docker rm -f db docker run -d --name db \ --mount type = volume,source = pgdata,target = /var/lib/postgresql/data \ postgres:16 # same data, new container Where do the bytes actually live? Under Docker's data root, typically /var/lib/docker/volumes/<name>/_data : docker volume inspect pgdata --format '{{ .Mountpoint }}' # /var/lib/docker/volumes/pgdata/_data The point is that you're not supposed to reach into that path directly — Docker owns it. You

Adapted from an appendix of my MS thesis. Markov Chain Monte Carlo Almost as soon as computers were invented, they were used for simulation. Markov chain Monte Carlo (MCMC) was invested as Los Alamos, Metropolis et al (1953) simulated a liquid in equilibrium with its gas phase. Their tour de force was the realization that they did not need to simulate the exact dynamics, they only needed to simulate some Markov chain with the same equilibrium distribution. The Metropolis algorithm was widely used by chemists and physicists, but was not widely known among statisticians until after 1990. Hastings (1970) generalized the Metropolis algorithm, and simulations following his scheme are said to use the Metropolis-Hastings (MH) algorithm [1]. A special case of the MH algorithm was introduced by Geman et al (1984) discussing optimization to find the posterior mode rather than simulation. Algorithms following their scheme are said to use the Gibbs sampler. It took some time for the spatial statistics community to understand that the Gibbs sampler simulated the posterior distribution, thus enabling full Bayesian inference of all kinds. Gelfand et al (1990) made the wider Bayesian community aware of the Gibbs sampler, and then it was rapidly realized that most Bayesian inference could be done using MCMC, whereas very little could be done without MCMC. Green (1995) generalized the MH algorithm as much as it could be generalized [1]. Theoretical Foundations A sequence X 1 ​ , X 2 ​ , … of random elements of some set is a Markov chain if the conditional distribution of X n + 1 ​ given X 1 ​ , … , X n ​ depends on X n ​ only. The set in which the X i ​ take values is called the state space of the Markov chain. A Markov chain has stationary transition probabilities if the conditional distribution of X n + 1 ​ given X n ​ does not depend on n . This is the main kind of Markov chain of interest in MCMC. The joint distribution of a Markov chain is determined by the following [1]. The ma

I shipped the first public build of a Chrome extension two weekends ago. The marketing-ready UI took me about six hours. The four state bugs below took me the rest of those two weekends, plus parts of the following week. I am writing this down because every reviewer of "I built an X in Y hours" posts seems to skip the state-model half, and the state-model half is where the actual time goes. The extension A sidebar that lives in Chrome's side panel API. You highlight text or screenshot a region on any page, the sidebar lets you pick a destination AI tab (ChatGPT / Claude / Gemini / a custom one) and forwards the content with a small wrapper prompt. That is the whole product description. The interesting part is what happens when a user does it twice. Bug 1: the destination you "logged into" is not the destination the message lands in First failure I caught: user has two ChatGPT tabs open, one workspace, one personal. The extension forwards to whichever tab was last focused. The user sees the message arrive in the workspace, replies there, then realizes the context they wanted to capture is on the personal tab. Fix: every AI destination registers a stable tab id at extension boot, not at click time. The forwarding logic walks the registry, not the focused window. Took a morning to redesign, an afternoon to migrate existing flows. Lesson: tab identity is not the same as window focus. Chrome's chrome.tabs.query({active: true}) returns the active tab. The active tab is not necessarily the destination the user has in their head. Bug 2: the screenshot is from before the user edited it User takes a screenshot of a code block, opens the sidebar, hits "annotate", drags a red box around lines 12-15, hits send. The annotation worked. But the underlying screenshot bytes were captured at the moment the toolbar first appeared, before the user could draw the box. Fix: the sidebar cannot trust that the screenshot in memory is the screenshot the user is looking at. Either re-capture o