DeepFrontend
Senior Frontend Engineering,
Demystified.
Master closures to React Server Components, event loops to WebSocket systems. Runnable code, under-the-hood mental models, and interview preparation for ambitious engineers.
// Simulating JS runtime concurrency
const loop = () => {
stack.push('fetchData');Call Stack
queue.push('callback');Callback Queue
};
// React 19 fiber reconciliation tree
const diff = (prev, next) => {
if (prev.type !== next.type) return replace(prev, next);
};
// Next.js incremental static cache fetch
fetch(url, { next: { revalidate: 3600 } })
.then(res => cache.set(url, res));
Curriculum
25 domainsCore Web
JavaScript
23The complete engine, scope, async, prototypes, memory, patterns, and the event loop.
Explore→CSS
16Layout, animation, architecture, and modern CSS features that show up in senior interviews.
Explore→TypeScript
15Types that scale, from daily usage to advanced generic patterns and declaration files.
Explore→Foundations & Tooling
11How the web actually works under the hood, assumed by most curricula, tested by senior interviews.
Explore→HTML
11Semantic markup, accessibility, HTML5 APIs, and everything interviewers actually probe.
Explore→Frameworks & State
React
25Hooks in depth, reconciliation, server components, concurrent features, and performance patterns.
Explore→Redux Ecosystem
19Redux Core, Redux Toolkit, Thunk, Saga, and when to reach for each.
Explore→Next.js
18App Router, rendering strategies, server actions, caching, and deployment.
Explore→State Management
4Atomic and signal-based state libraries, when to use them over Redux or Context.
Explore→Backend & APIs
Node.js
16The runtime, event loop, streams, auth, and scaling strategies.
Explore→Databases
14MongoDB, SQL/PostgreSQL, Prisma ORM, Redis, and when to choose what.
Explore→API Development
13REST, WebSockets, OAuth, sessions, and API design best practices.
Explore→Express.js
11REST APIs, middleware, auth, security, and MVC patterns in Express.
Explore→GraphQL
9Schema design, Apollo, federation, N+1, and security.
Explore→Backend for Frontend (BFF)
4API Gateway, BFF pattern, auth flow, caching, and aggregation strategies.
Explore→Engineering Practices
Frontend Performance
11Core Web Vitals, runtime profiling, bundle analysis, and measurable optimization techniques.
Explore→Frontend Architecture
11Monorepos, micro frontends, design systems, i18n, observability, and CI/CD.
Explore→Testing
9Unit, integration, E2E, mocking, and testing strategy from pyramid to trophy.
Explore→Web Security
7XSS, CSRF, CSP, CORS, OWASP Top 10, the security layer senior engineers are expected to own.
Explore→DevOps & Deployment
5Docker, CI/CD, hosting, secrets, and monitoring for frontend and Node apps.
Explore→PWA & Offline
5Service workers, caching strategies, installability, and offline-first architecture.
Explore→Career & Emerging Tech
System Design
25Scalability, CDN, queues, real-time systems, and frontend system design for senior interviews.
Explore→Data Structures & Algorithms
18A structured, progressive curriculum from fundamentals to advanced problem-solving.
Explore→AI for Frontend Developers
10AI SDK, prompt engineering, RAG, MCP, tool calling, and production AI patterns.
Explore→Interview Prep
5DSA for frontend, machine-coding patterns, behavioral interviews, resume, and negotiation.
Explore→Try it right now
No signup. Real code, real tests, graded in your browser, right here on this page.
Run your code to see results.
Interview-grade depth
Every topic goes Concept → Under the Hood → Common Mistakes. The mental model a senior engineer actually needs.
Runnable, not read-only
Interactive step-through visualizers and live, editable code sandboxes embedded directly in each lesson.
Real interview prep
Tiered interview questions and model answers, junior through staff, plus real follow-ups interviewers ask.
Practice that's graded
Auto-graded coding challenges in The Forge with real tests run in your browser and instant feedback.
Free to start
No account needed. Dive in.
Event Loop
JavaScript is single-threaded, yet it handles timers, network requests, and UI events without blocking. The event loop is the mechanism that makes this possible, and its exact rules (microtasks before macrotasks, always) explain nearly every 'why did this run in that order' question you'll ever debug.
Reconciliation & the Virtual DOM
The Virtual DOM isn't a performance trick, it's a comparison mechanism. React diffs the new element tree against the last one it committed, and the ONE piece of information that diff runs on is each element's type plus its key. Nearly every list bug and every reconciliation interview question traces back to that single fact.
Caching (Cache Components + legacy model)
Nearly every widely-known 'four cache layers' explanation of Next.js caching describes a model that is now explicitly the Previous Model. Cache Components, "use cache" plus cacheLife/cacheTag/updateTag/revalidateTag, is the current one, and it answers the exact same question (what's cached, for how long, and how do I invalidate it on demand) with one directive instead of four separate systems to reason about.
Generics
A plain generic function called with ["a", "b"] infers T as the widened `string`, but mark the type parameter <const T> (stable since TypeScript 5.0) and the exact same call infers the literal tuple instead, confirmed by compiling both side by side. This flagship topic covers generics from first principles through that specific, often-missed modern capability.
Event Loop & libuv
The browser's event loop (macrotasks vs. microtasks) is only half the story in Node.js, libuv adds six distinct phases, and process.nextTick sits in its own queue with HIGHER priority than promises, draining completely between every single phase transition. This flagship topic walks all of it step by step.
HTTP Server Fundamentals
req and res aren't special HTTP-only objects, req is a Readable stream and res is a Writable stream, the exact same primitives from Streams & Buffers wearing HTTP clothing. Understanding that turns 'how does Express work' from a black box into a direct application of mechanics you already know.
What is Free vs What Requires an Account
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Always Free for Everyone
Read and practice immediately without ever giving us an email or creating a password.
- ✓All 315 concept & architecture guides
- ✓132 hands-on coding challenges
- ✓All interactive visualizers & sandboxes
- ✓In-browser local progress tracking
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DeepFrontend Pro
For engineers who want on-demand AI code reviews and personalized mock interview scoring.
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- ✓Interactive AI Code Tutor for all 132 challenges
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Ready to go deep?
315+ topics across 25 domains, 133 graded challenges, 2,412+ active-recall questions, zero fluff.