Frontend System Design: Build an Autocomplete
A structured walkthrough of the autocomplete design round: requirements, architecture, race-free fetching, caching, rendering, the ARIA combobox and metrics.
~7 min readread →
psst… 1300+ questions inside
Your interview study notes, finally organized.
Clear, friendly notes on the JavaScript, TypeScript, React & Angular questions that come up again and again, with the reasoning written in the margins. Then practice them like it's the real interview.
Closures, Ch. 1 ✦
function outer() { let count = 0; return function inner() { return ++count; }; } const next = outer(); next(); // 1 next(); // 2 ← why not 1?!
Q: var vs let?var → function scope, hoisted as undefined
let → block scope + TDZ!
let → block scope + TDZ!
Top 10 Q ★Asked in almost every JS round.
Pick a chapter (start anywhere, really)
See all chapters →Frontend
The browser, the language and the frameworks.JSCh. 01
JavaScript
Closures, hoisting, prototypes & the event loop.
TSCh. 02
TypeScript
Generics, narrowing, utility & mapped types.
ReactCh. 03
React
Hooks, rendering, memoization & state.
AngularCh. 04
Angular
Change detection, DI, signals & RxJS.
HTML/CSSCh. 05
HTML & CSS
Semantics, the box model, layout & a11y.
{ }Bonus
Coding round
Debounce, Promise.all, LRU cache… write it, run the tests.
Backend
Servers, services and the languages behind them.NodeCh. 06
Node.js
Event loop phases, streams & modules.
JavaCh. 07
Java
OOP, collections, JVM, concurrency & streams.
SpringCh. 08
Spring Boot
IoC, auto-configuration, JPA, REST & security.
PythonCh. 09
Python
Data model, generators, decorators & the GIL.
MicroCh. 10
Microservices
Service design, messaging, resilience & sagas.
Databases
Relational and document stores, queries and design.Cloud & DevOps
Containers, orchestration, cloud and delivery.Platforms
Enterprise platforms with their own interview loops.Fundamentals
Algorithms and architecture: asked everywhere.The practice room no sign-up, saved in your browser
Open the practice room →Quiz369 multiple-choice & “what's the output?” questions, with explanations.Flashcards940 cards with spaced repetition, so they stick.Mock interviewTimed questions, model answers and a score report.Coding round14 challenges with tests that run in your browser.
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Latest notes fresh off the pen ✎
All 19 notes →Closures, Scope & the Classic setTimeout Loop
What lexical scope and closures really are, why the var + setTimeout loop prints 3 3 3, three ways to fix it, and where closures earn their keep in real code.
~6 min readread →
TypeScript Generics, Explained Through Interview Questions
Ten generics questions, from constraints and keyof to infer, distributive conditional types and variance, each with a short answer and code you can reproduce.
~6 min readread →
The Event Loop: Microtasks vs Macrotasks
How the call stack, task queue and microtask queue fit together, where rendering happens, how async/await schedules work, and output puzzles with answers.
~7 min readread →
useEffect Pitfalls Interviewers Love to Ask
Stale closures, missing cleanup, fetch races, Strict Mode's double run, infinite loops and effects you don't need, plus how useLayoutEffect differs in timing.
~7 min readread →
The this Keyword: Four Binding Rules and One Exception
How JavaScript decides what this refers to: default, implicit, explicit and new binding, the order they win in, why arrow functions ignore them, and the bugs that follow.
~6 min readread →
Tear-off cheat sheets print & stick on your wall
All cheat sheets →A note in your inbox, every Sunday.
One tricky interview question, fully explained. Takes 5 minutes to read with your coffee.