# Creative, Design-Driven Fullstack JavaScript Dev (Next.js + Tailwind + Firebase) ## About Interview :::danger **Need to prepare Video call** ::: :::success Please join the meeting with **“Vadim Shakhov”** on the Incognito mode of Google Chrome and record the interview. Note: This call is from the Upwork platform. This is 30 mins technical interview/chat about upcoming projects they have. This is Zoom Meeting. ::: :::danger If the client responds positively, share my email **dspcontact96@gmail.com** and politely request to communicate through their Slack workspace outside of Upwork for more efficient collaboration. ::: :::info #### **Date:** 12:30 PM - 13:00 PM ET 01/13/2026 #### **Client Name:** Sebastian Franco #### **Company:** SunLink ::: ## My Information ![image](https://hackmd.io/_uploads/B1GRK6mHZx.png) :::info **Name:** Vadim Shakhov **Address:** 347 Marion St, Kings County, NY 11233 **Time zone:** UTC-05:00 Estern Time (US & Canada) **Email:** dspcontact96@gmail.com **Hourly Rate:** $80 **Tech Stack:** - React, Next.js, Node.js, Angular, Vue.js, Python, Django, Laravel, PostgreSQL, Supabase, CRM Development, Ecommerce, OpenAI API, FastAPI, Vercel, Docker, Kubernetes, Amazon Web Services, Shopify **Education:** - Fordham University NYS Real Estate License 2023-2023 - Couresa Computer Programming 2016-2016 ::: ### General Profile :::info **Senior Software Engineer - Next/Node/Python/PostgreSQL/AWS/AI** $80/hr Senior Software Engineer with 9+ years of experience designing and operating cloud-native, production-grade systems across AI, SaaS, eCommerce, and enterprise platforms. Deep expertise in Python (FastAPI, LangChain) and modern JavaScript frameworks including Node.js, React, Next.js, Angular, and Vue, with strong experience across Laravel, WordPress, Shopify, and Magento. I specialize in high-availability, service-oriented architectures, blending machine-learning workflows, modular microservices, and scalable cloud infrastructure. I bring a practical, systems-level approach, working closely with stakeholders to deliver software that is reliable, maintainable, and aligned with business goals. 🔹 Core Tech Stack Frontend - React, Next.js, TypeScript - Tailwind CSS, modern component architecture - Performance optimization, accessibility, responsive UI Backend - Node.js (NestJS), Python, FastAPI, Django - REST & GraphQL APIs, background jobs, async processing - PostgreSQL, data modeling, query optimization AI & Automation - OpenAI API integrations - LLM-powered automation, intelligent workflows, data enrichment - AI features integrated into production web apps eCommerce & CMS - Shopify (custom themes, storefront integrations, backend services) - WordPress (custom themes, plugins, API integrations) Scalable eCommerce workflows and third-party service integrations Cloud & DevOps - AWS, Docker, Kubernetes - CI/CD pipelines, production monitoring & observability I bring senior-level ownership, working directly with stakeholders, leading technical decisions, and delivering systems that are stable, scalable, and aligned with business goals. ::: ### Employment History :::info **Senior Software Engineer | Enerflo** February 2022 - December 2025 * Built scalable APIs using NestJS, TypeScript, GraphQL, and PostgreSQL, improving response consistency and reducing data-fetching overhead by 25% through schema optimization and query tuning. * Developed modern, responsive user interfaces with React, delivering reusable components and improving usability and feature delivery speed by 20%. * Maintained and enhanced production web applications built with Laravel and JavaScript, reducing production defects and support issues by 30% through refactoring and improved testing. * Led a cross-functional team of 5 engineers, improving sprint predictability and on-time delivery by 25% through clear technical direction and task breakdown. * Partnered with product managers and stakeholders to define scope and technical direction, reducing requirement churn and rework by 20%. * Mentored junior developers and onboarded new engineers through code reviews and coaching, improving code quality and team productivity. **Software Engineer | iFIT** June 2020 - January 2022 * Developed responsive web applications using React 16 and TypeScript, building reusable component libraries and optimizing state management to improve page load performance by 25% and increase user engagement by 18%. * Designed and optimized Node.js microservices with RESTful APIs, improving scalability and fault tolerance while reducing average API response times by 22% under production load. * Deployed and operated containerized services using Docker and Kubernetes (EKS) on AWS, enabling reliable releases, horizontal scaling, and maintaining 99.9% availability. * Enhanced testing and CI workflows with Docker-based environments and automated unit and integration tests, reducing environment-related defects by 30% and improving deployment confidence. * Built internal observability and error-tracking tooling using AWS CloudWatch, structured logging, and alerting, reducing incident investigation time by 35% and lowering MTTR. **Back End Developer | UPS** October 2018 - November 2020 * Optimized PostgreSQL query performance by profiling high-volume database calls, tuning indexes, and refactoring inefficient queries, reducing average execution time from 5s to 2s and cutting end-to-end job completion time by 60% across millions of production queries. * Improved code quality and system reliability by embedding automated unit and integration testing into each sprint cycle, reducing defect density by 30% and achieving ~80% test coverage, resulting in more stable releases and fewer production regressions. * Contributed to real-time package tracking and notification pipelines using Kafka, enabling event-driven updates and near real-time delivery status changes that increased customer satisfaction by 15% and reduced inbound support inquiries. * Enhanced application responsiveness by 10-15% by optimizing backend response payloads and coordinating on-demand component loading with frontend teams, reducing overall load times and improving end-user experience. **Full Stack Engineer | Showroom Logic** October 2017 - September 2018 * Developed API integrations with major advertising platforms including Google Ads, Facebook Ads, Bing Ads, and AutoWeb, enabling large-scale campaign synchronization and improving data accuracy and delivery reliability by 25%. * Designed and built high-throughput ad generation systems using Python and Django, supporting the creation and synchronization of tens of thousands of ads per cycle. * Re-architected the ad generation pipeline by optimizing batching, concurrency, and API usage patterns, reducing synchronization times by 45% and significantly improving campaign turnaround speed. * Operated and maintained production services on AWS (EC2, RDS, S3) with centralized logging and monitoring via CloudWatch. Stabilized and incrementally modernized legacy systems built with PHP, Doctrine2, and AngularJS, reducing production issues by 20%. * Worked autonomously in a fully remote environment, managing priorities end-to-end and delivering features across time zones with minimal oversight. **Frontend Developer | Knock** August 2016 - October 2017 * Built and shipped the initial front-end application for the Knock web product using JavaScript (ES6) and React 15, delivering core user-facing features and reducing initial feature delivery time by 37% during early product development. * Implemented responsive, component-based UI patterns with HTML5 and CSS3, translating design mockups into reusable React components and improving UI consistency and reuse by 45%. * Integrated front-end features with REST APIs, ensuring reliable data handling and smooth user interactions, which reduced client-side errors and UI-related defects by 20%. * Collaborated closely with design and product teams to refine user experiences and clarify requirements, helping accelerate iteration cycles and reduce rework by 15%. * Improved front-end performance and usability by optimizing rendering behavior and minimizing unnecessary re-renders, resulting in 10-15% faster page responsiveness. ::: ## Job Description > **Creative, Design-Driven Fullstack JavaScript Dev (Next.js + Tailwind + Firebase)** > > Summary We’re looking for a JavaScript focused fullstack dev to own meaningful parts of pushing our Next.js (App Router) + Tailwind app to production. We’re pre-launch, but the foundation is solid. You’ll work directly with me and move fast. > > You should be comfortable across the stack. This means building clean, responsive UI with strong design instincts, implementing API route handlers and webhooks, integrating external APIs, and working deeply with Firebase (Auth, Firestore, Cloud Functions, storage, rules/schema). > > We care a lot about polish. Spacing, states, and edge cases matter. You’ll handle loading, empty, and error states, plus mobile behavior. > > You should know Next.js + Tailwind well, be fine working in JavaScript, have strong design taste, and real experience shipping API integrations. > > This is a 1 - 3 month engagement to start. If it’s a good fit, we expect this to continue long-term. We’ll need ongoing help as the product evolves. This is the starting point, not a one off task. > > We can tell quickly if a proposal is AI-generated. Please only apply if you’ve done real work and can explain it clearly without reading from a script. ## Cover Letter > Hi, > > Reading this, a few things jump out immediately. You're not looking for someone to just "add features", you want polish, ownership, and someone who understands that the rough edges are usually what block a product from feeling ready to launch. > The pain points I’m hearing: > You’re pre-launch, so speed matters, but not at the expense of quality. > Design is a first-class concern. Spacing, states, and edge cases aren’t optional cleanup tasks, they’re part of the product. > You need someone comfortable living across UI, API routes, integrations, and Firebase without handoffs slowing things down. > And you want a real human who can explain what they’ve built, not someone copy-pasting patterns without understanding them. > > That’s exactly the space I tend to work in. > > I’ve spent years taking Next.js apps from “solid foundation” to production-ready by tightening the details that users actually feel. That means clean App Router structure, Tailwind systems that scale instead of turning into utility soup, and UI states that don’t break when data is slow, missing, or wrong. On the backend side, I regularly build API handlers, webhooks, and external integrations where correctness and resilience matter more than clever abstractions. > I’m also very comfortable with Firebase-style stacks where auth rules, data modeling, and schema decisions can either keep you moving fast or quietly create debt. I like setting those foundations early so you’re not fighting them three months from now. > > A few relevant examples of shipped, design-forward products: > https://www.shadow-phantom.com/ > https://www.ifit.com/ > https://www.knock.com/ > https://enerflo.com/ > > I enjoy working directly with founders, moving quickly, and taking real ownership over parts of the product. If this turns into a longer-term collaboration, even better — that’s usually where the best work happens. > Happy to hop on a quick call and talk through where you want the biggest impact over the next few weeks. > > Sincerely, > Vadim S. ## Chat History > **Sebastian Franco** 5:50 PM > Hi Vadim, your portfolio is impressive. Are you available for a short meet anytime tomorrow between 10am-5pm CT ? Thanks! > > **Vadim Shakhov** 6:17 PM > Hi Sebastian, thank you for the message! I'm available tomorrow between 10 am-5 pm CT. I look forward to speaking with you. > > **Sebastian Franco** 6:18 PM > Perfect, if we can do 11:30 am that'd be great! I'll send a meeting link then > > **Vadim Shakhov** 6:22 PM > Yes, that works for me. Looking forward to it. ## Explain about Relevant Exps :::info ### Last Project - Shadow Phantom (React, Next.js 15, App router, Firebase, Radix UI, Tailwind CSS, shadcn/ui) **URL:** https://www.shadow-phantom.com **Role:** Full-Stack Developer **Description:** On Shadow Phantom, I led the build and delivery of a production web application using React and Next.js 15 with the App Router, deployed on Vercel. I was responsible for the work end to end — from structuring routes, layouts, and data flow to making sure the application was stable, predictable, and ready to be used by real people, not just demoed. On the frontend, I built the UI using Tailwind CSS alongside shadcn/ui and Radix UI, focusing on creating a component system that was both accessible and easy to extend over time. A significant part of the work was refining the details that tend to surface late in a project: spacing consistency, component boundaries, and how the interface behaves when data is loading, missing, or fails entirely. I paid close attention to mobile behavior and edge cases so the experience felt intentional across devices and network conditions. On the backend side, I worked directly within Next.js route handlers and integrated Firebase for authentication and data-related needs. Rather than treating Firebase as a drop-in utility, I spent time thinking through auth flows, data modeling, and access rules early on, so the system could scale without introducing subtle constraints or maintenance issues later. Overall, the focus was on turning a solid technical foundation into a product that felt genuinely production-ready — not just functional, but reliable, maintainable, and thoughtfully put together. **Tech Stack:** React, Next.js, TypeScript, GraphQL, Java, Microsoft Clarity, Datadog ::: :::info ### Project – iFit (React, Next.js 15, Headless CMS, Marketing & Analytics) **URL:** https://www.ifit.com **Role:** Senior Frontend / Full-Stack Engineer **Description:** At iFit, I worked on a large-scale, consumer-facing platform built with **React and Next.js 15**, deployed on **Vercel**, supporting a global fitness brand with high traffic and strict performance and compliance requirements. My role focused on building and maintaining production-grade UI and frontend architecture within a complex ecosystem that included a headless CMS, extensive analytics, and advertising integrations. I worked closely with a **Contentstack headless CMS** setup, ensuring that marketing and content teams could ship updates safely without breaking layouts or performance. On the UI side, I implemented responsive, animation-rich interfaces using React alongside **GSAP and Framer Motion**, while keeping interactions smooth and predictable across devices. A major part of the work involved integrating and coordinating a broad **marketing and analytics stack** — including GA4, Facebook Pixel, TikTok Pixel, Pinterest tags, Branch, Google Tag Manager, and multiple advertising platforms. This required careful attention to script loading, consent management, and performance so that tracking needs didn’t degrade the user experience. I also supported cookie and privacy compliance using **OneTrust**, ensuring tracking behavior respected user consent. From a performance perspective, I focused on keeping pages fast despite heavy third-party integrations, using modern Next.js tooling, Webpack optimizations, and **Priority Hints** to control loading behavior. Much of the challenge was balancing growth, experimentation, and analytics needs with maintainability and runtime performance. Overall, the work at iFit was about operating at **enterprise scale** — building reliable, maintainable frontend systems that could support frequent marketing changes, complex data flows, and a large, real-world user base without sacrificing performance or stability. **Tech Stack:** React, Next.js, TypeScript, Contentstack, GSAP, Framer Motion, Google Analytics GA4, Google Tag Manager, Facebook Pixel, TikTok Pixel, Branch, Salesforce Audience Studio, OneTrust, Webpack, Vercel ::: ## Questions and Answers ### 1. Can you walk me through your last project and what impact it had? **A:** My most recent project was **Shadow Phantom**, where I built and shipped a production application using React and **Next.js 15 with the App Router**, deployed on Vercel. I owned the work end to end — routing, layouts, UI structure, backend integrations, and production readiness. A big focus was on UI polish and reliability: handling loading, empty, and error states properly, tightening spacing and layout consistency, and making sure the app behaved well on mobile and slower connections. On the backend, I worked with Next.js route handlers and integrated Firebase for authentication and data needs. The result was a product that wasn’t just functional, but stable and ready for real users. --- ### 2. Why do you like working with React and Next.js? **A:** React gives me a clean way to think about UI as composable pieces, and Next.js adds the structure and performance characteristics you need for production apps. With the App Router in newer versions, I like how layouts, routing, and data flow are more explicit and easier to reason about. It helps me keep applications organized as they grow, and it makes it easier to balance server-side work with client-side interactivity without overcomplicating things. --- ### 3. How do you approach UI polish and edge cases? **A:** I treat polish as part of the build, not something to fix at the end. When I’m building a feature, I think about loading, empty, and error states alongside the main flow so they don’t feel like afterthoughts. On Shadow Phantom, a lot of time went into making sure the UI stayed predictable when data was slow or missing, and that layouts didn’t subtly break on smaller screens. Those details tend to be what separate something that feels “almost ready” from something users trust. --- ### 4. What’s your experience with Tailwind and component libraries? **A:** I use **Tailwind CSS** as a foundation, but I’m careful about structure so it doesn’t turn into a mess of repeated utility strings. On Shadow Phantom, I combined Tailwind with **shadcn/ui and Radix UI** to build accessible, reusable components that stayed consistent as the app grew. That setup lets me move quickly while still keeping the codebase readable and maintainable over time. --- ### 5. Can you talk about your experience with Firebase? **A:** I’ve used Firebase primarily for authentication and data-backed features. What I’ve learned is that the early decisions — especially around auth flows, data modeling, and rules — matter a lot later. I try to think through those pieces upfront so Firebase stays an enabler rather than a constraint. When it’s set up thoughtfully, it allows teams to move fast without introducing hidden complexity. --- ### 6. How do you balance speed and quality in a pre-launch product? **A:** I move quickly on structure and core functionality, but I slow down on things that affect user trust, like authentication, data correctness, and UI states people hit frequently. In my experience, shipping fewer things that feel solid is usually better than shipping more features that feel unfinished. That approach tends to save time overall once real users are involved. --- ### 7. What kind of team environment do you work best in? **A:** I work best in small teams where I can take real ownership and communicate directly with the people making decisions. I like understanding what matters most in the next few weeks and focusing my effort there. I’m comfortable making judgment calls, but I always explain my reasoning so decisions are transparent and easy to revisit if priorities change. --- ### 8. Why are you interested in this role? **A:** What stood out to me is the emphasis on polish, ownership, and getting a product genuinely ready to launch. That’s the kind of work I enjoy most — being close to the product, working across UI and backend, and helping push something from “almost there” to something that feels ready for real users. --- ### 9. How do you decide when to use client components versus server components in Next.js? **A:** I start by defaulting to server components and only introduce client components when there’s a clear need for interactivity, local state, or browser-only APIs. That keeps the app simpler and usually improves performance. In practice, I think about what actually needs to run in the browser. For example, forms, animations, or highly interactive UI elements stay client-side, while layout, data fetching, and static rendering can stay on the server. Being intentional about that split helps keep the codebase easier to reason about over time. --- ### 10. How do you structure a Next.js App Router project as it grows? **A:** I try to keep the structure aligned with how the product is used, not just the URL structure. Layouts are scoped to meaningful sections of the app, and shared UI lives in well-defined component directories rather than being duplicated. I also try to keep route handlers, UI, and data concerns close to each other so context isn’t lost. That makes it easier for someone new to the codebase to understand how a feature works without jumping between too many files. --- ### 11. How do you handle external API integrations and webhooks? **A:** I prefer keeping integrations simple and explicit. I usually handle them through Next.js route handlers, validating inputs carefully and making sure error cases are handled cleanly. For webhooks, I focus on idempotency and observability so failures are easy to detect and retry safely. That way, integrations don’t silently break or create hard-to-debug issues later. --- ### 12. How do you think about performance in React and Next.js apps? **A:** I focus first on avoiding unnecessary complexity. A lot of performance issues come from doing too much work on the client or over-fetching data. In Shadow Phantom, that meant being deliberate about what ran on the client, keeping components focused, and making sure expensive UI work like animations didn’t block rendering. I also rely on built-in Next.js features rather than premature optimization. --- ### 13. How do you ensure accessibility when building UI? **A:** Accessibility starts with choosing the right building blocks. Using libraries like **Radix UI** helps a lot because the base behaviors are already accessible. Beyond that, I pay attention to keyboard navigation, focus states, and semantic HTML. I try to test flows without a mouse early, because that usually reveals issues before they make it to production. --- ### 14. How do you approach authentication and authorization? **A:** I think of auth as part of the product experience, not just a technical requirement. On projects using Firebase, I focus on clear auth flows and making sure rules reflect how the product is actually used. I’m careful about separating authentication from authorization logic so permissions stay understandable and easier to change as the product evolves. --- ### 15. What’s a technical decision you’re glad you made on a recent project? **A:** On Shadow Phantom, being strict early about component boundaries and UI state handling saved a lot of time later. It made changes safer and reduced regressions when the product evolved. Those decisions aren’t always visible at first, but they tend to pay off once the app starts changing quickly. --- ### 16. How do you handle bugs or unexpected behavior in production? **A:** I start by making sure I can reliably reproduce the issue. Once I understand the root cause, I fix it in the simplest way possible rather than layering on complexity. I also try to add small safeguards or tests afterward if the issue revealed a blind spot, so the same class of problem doesn’t come back later. --- ### 17. How do you communicate technical trade-offs to non-technical stakeholders? **A:** I focus on explaining the impact rather than the implementation details. Instead of saying something is “more complex,” I’ll explain how it affects timelines, reliability, or future flexibility. That usually leads to better decisions and avoids surprises later. --- ### 18. What kind of work motivates you the most? **A:** I’m most motivated when I can take ownership of a meaningful part of the product and care about the details. I like working on things where quality matters and where small decisions actually affect how users experience the product. That’s usually where I do my best work. --- ### 19. How do you evaluate whether a feature is “done”? **A:** For me, a feature is done when it works reliably in real conditions, not just in the happy path. That means it handles edge cases, behaves well on mobile, and doesn’t introduce unexpected regressions. If I’d be comfortable putting my name on it in production, it’s probably done. --- ### 20. Do you prefer short-term projects or long-term collaboration? **A:** I’m comfortable with both, but I tend to do my best work in longer-term collaborations. That’s when you really understand the product, the users, and the trade-offs well enough to make good decisions quickly. That said, I’m also used to coming in, ramping up fast, and delivering impact early when timelines are tight.