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Lessons (40)

• React vs Vue vs Angular

  The same counter in three frameworks, a side-by-side comparison of reactivity, templates, state and tooling, and …

• Count, for_each, Functions, and Stable Identities

  … Use a moved block when you intend to preserve the original object under a new address. count remains …

• JavaScript Essentials: Event Loop, Closures & this

  … a separate backpack mermaid flowchart LR MC["makeCounter() runs<br/ creates count = 0"] -- F["returns increment()"] F -- BP …

• Hash Maps & Sets

  … string/symbol keys only; fine for simple records const counts = {}; counts["a"] = (counts["a"] ?? 0) + 1; 💡 Prefer Map …

• Sorting Algorithms

  … toSorted() (ES2023) const sorted = prices.toSorted((a, b) = a - b); Counting sort: beating n log n Comparison sorts …

• KISS: Keep It Simple, Stupid

  … Simplify conditions js // ❌ function getShippingCost(country) { if (country === "US") { return 5; } else if (country === "CA") { return 8; } else …

• SQL Language, Identifiers & Data Types

  … A sequence is a reusable database counter. UUIDs can be generated without a central counter and help distributed …

• React Fundamentals

  … Counter() runs again with count = 1 C-- R: new JSX R- R: diff old vs new R- D …

• Database Indexing & Transactions

  … by country, then city, then age. sql CREATE INDEX idx people location ON people (country, city, age); Query …

• Arrays & Strings

  … count[ch] = (count[ch] ?? 0) + 1; for (const ch of b) { if (!count[ch]) return false; count[ch …

• Data Structures for Scale

  … Measure memory, query latency, false-positive rate and count error; “smaller” is useful only if the error contract …

• SQL Interview Query Drills

  … Find repeated rows SELECT name, section, COUNT( ) AS copies FROM students GROUP BY name, section HAVING COUNT( ) 1 …

• 10,000 Users Do Not Need 10,000 Database Connections

  … Tune from database saturation and query behavior, not user count alone. Walk through a failure and recovery A …

• CloudWatch: Know What Your App Is Doing

  … To count failures by operation: text fields operation, status code filter status code = 500 stats count() as failures …

• Rust: Types, Errors and Concurrency

  … Vec< = (0..8) .map( { let counter = Arc::clone(&counter); thread::spawn(move { counter.lock().unwrap() += 1; }) }) .collect(); for …

• REST vs GraphQL vs gRPC

  … GET /users/42/followers/count API-- App: count Note over App: 3 round trips on a slow 4G …

• Trees & Binary Search Trees

  … empty tree return 1 + Math.max(height(node.left), height(node.right)); // combine } // Count nodes const count = (node …

• Recursion & Backtracking

  … countdown js function countdown(n) { if (n === 0) { // base case console.log("🚀 Liftoff!"); return; } console.log(n); countdown …

• GitOps, Progressive Delivery and Observability

  … queue length, Kafka lag, cron, with scale to zero Cluster Autoscaler / Karpenter Node count; Karpenter picks the cheapest …

• Python and Math Foundations with Runnable Examples

  … These hand-written vectors demonstrate the calculation without pretending to provide semantic understanding. Count classification mistakes Suppose a …

• Creational Patterns: How to Make Objects

  … Builder 🍔 Analogy: At a burger counter you build your order step by step: bun → patty → cheese → no onions …

• Hexagonal Architecture (Ports & Adapters)

  … Promise<void ; countActiveFor(memberId: string): Promise<number ; } export interface Notifier { loanConfirmed(memberId: string, loan: Loan): Promise<void ; } export …

• AWS Data Pipelines in Plain Language

  … Record input version, transformation version, output location, and row counts. Re-running a job for the same input …

• Batch vs Stream and Data Modeling

  … Measure stream freshness, late-event count and reconciliation differences; streaming speed is useful only when outputs are correct …

• Capacity, Availability, Latency and CAP

  … Payments/inventory normally reject uncertain writes; feeds/counters can serve a stale value. CAP is about partitions, not …

• Go Concurrency: Goroutines, Channels and Context

  … each iteration has its own url }() } wg.Wait() // block until the counter reaches zero ⚠️ Before Go 1.22 …

• Deploying & Operating Microservices

  … user.id, country: user.country })) { return renderNewCheckout(); } return renderOldCheckout(); mermaid flowchart LR D["🚀 Deploy<br/ (code is in …

• Python Fundamentals

  … start = time.perf counter() try: return fn( args, kwargs) finally: print(f"{fn. name } took {time.perf counter …

• Go Fundamentals

  … total } counter := func() func() int { // closure n := 0 return func() int { n++; return n } }() counter(); counter() // 1, 2 …

• Resilient Service Calls: Retries, Breakers and Load Shedding

  … Measure attempts per original request, queue age, successful throughput and unrelated-endpoint latency; a low downstream call count …

• Concurrency, Resilience & Distributed Workflows

  … available 0 RETURNING available; If the returned row count is zero, the reservation failed. For more involved work …

• Capacity Planning, SLOs and Error Budgets

  … responses, so latency looks good while checkout fails. Count success and latency together, and compare budget consumption to …

• Rust: Ownership, Borrowing and Lifetimes

  … f64 = 9.99; // explicit type println!("{name} {count} {price:.2}"); } Rule 1: every value has one owner rust …

• Production Capstone and Interview Practice

  … Ephemeral and supported write-only mechanisms address persistence. When use for each instead of count? When stable named …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … No separate cluster needed; it runs inside your service. java // Count orders per customer in 1-minute windows …

• Caching & Redis

  … Its data types solve many real problems: Type Commands Use case --- --- --- String SET , GET , INCR , EXPIRE Cache, counters …

• Graphs: BFS & DFS

  … Each cell is a node; its neighbours are up, down, left and right. Number of islands: count groups …

• TypeScript Essentials

  … you rarely need to write the type let count = 5; // inferred as number count = "five"; // ❌ error Type Meaning …

• Microkernel (Plugin) Architecture

  … Claims or tax engine One plug-in per country or state's rules The parts mermaid flowchart TB …

• Scaling, Load Balancing & Rate Limiting

  … window Count per minute (resets at :00) Simple; allows 2× bursts at window edges Sliding window Count over …